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ELEMENTS  OF  BIOLOGY 


A  PRACTICAL  TEXT-BOOK  COR- 
RELATING BOTANY,  ZOOLOGY, 
AND     HUMAN     PHYSIOLOGY 


BY 


GEORGE   WILLIAM    HUNTER,  A.M. 

Head  of  the  Depaktment  of  Biology,  De  Witt  Clinton  High  School, 

New  York 


NEW  YORK  .:.  CINCINNATI  •:•  CHICAGO 

AMERICAN    BOOK    COMPANY 


COPYKIQHT,    1907,    BY 

GEORGE  WILLIAM  HUNTEE. 


nUNTEE,    BIOLOGY. 
W.   P.    II 


THE  PURPOSE   AND  PLAN   OF  THIS  BOOK 

The  aim  of  this  book  is  to  correlate  the  allied  subjects  of  botany, 
zoology,  and  human  physiology  in  a  general  course  of  biology  for  the 
first  year  of  the  high  school.  The  foundation  principles  upon  which 
this  correlation  is  made  are  that  the  life  processes  of  plants  and  of 
animals  are  similar,  and  in  many  respects,  identical ;  that  the  prop- 
erties and  activities  of  protoplasm  are  the  same  whether  in  the  cell 
of  a  plant  or  of  an  animal ;  and  that  the  human  body  is  a  delicate 
machine  built  out  of  that  same  mysterious  living  matter,  protoplasm. 
With  such  a  foundation  correlation  is  not  only  possible,  but  natural. 

The  following  pages  are  the  results  of  my  experience  with  large 
classes  of  young  students  in  the  first  year  of  the  high  school.  The 
average  age  of  such  pupils  is  about  fourteen  years.  To  such  pupils 
the  life  activities  of  plants  and  animals  have  an  appealing  interest ; 
simple  experiments  in  plant  physiology  are  performed  with  never 
failing  zest.  Laboratory  and  field  work,  so  far  as  they  relate  to 
adaptations  to  functions,  are  readily  comprehended. 

For  young  students  laboratory  questions  should  be  simple  and 
few ;  they  should  apply  to  structures  easily  found,  and  deal  with  ex- 
ternals only.  Minute  directions  are  necessary  in  order  to  insure  the 
successful  working  out  of  the  given  problem.  The  form  of  the  lab- 
oratory questions  must,  after  all,  be  left  to  the  individual  teacher. 
The  paragraphs  on  laboratory  work  which  follow  are  suggestions. 
Eor  formal  directions  in  botany  and  zoology  according  to  the  note 
and  question  method,  the  reader  is  referred  to  Hunter  and  Valentine, 
Laboratory  Manual  of  Biology,  Henry  Holt  and  Company.  For  lab- 
oratory exercises  in  human  anatomy  and  physiology,  Eddy,  Expert- 


6  THE  PURPOSE  AND   PLAN   OF   THIS   BOOK 

mental  Physiology  arid  Anatomy,  American  Book  Company,  will  be 
found  useful. 

The  following  chapters  contain  such  material  as  has  been  found 
by  most  teachers  of  first-year  biology  to  be  sufi6.cient  for  a  well- 
rounded  course  in  the  first  year  of  the  high  school.  In  selecting 
material,  the  syllabuses  for  elementary  botany,  zoology,  and  human 
physiology  given  by  the  New  York  State  Education  Department 
have  been  followed.  It  would  not  be  wise  to  attempt  all  of  the  work 
outlined  in  this  book.  Work  should  be  attempted  only  with  such 
materials  as  are  easily  obtainable  in  a  given  locality.  It  is  thought 
that  each  successive  chapter,  although  related  to  that  immediately 
preceding  it,  is  yet  distinctive  enough  to  allow  of  the  omission  of  a 
chapter  or  chapters  without  in  any  way  interfering  with  the  conti- 
nuity of  the  work. 

Two  styles  of  type  have  been  used.  The  larger  type  contains 
material  which  is  believed  to  be  of  first  importance,  the  smaller  type 
the  less  important  topics.  Suggestions  for  laboratory  exercises  are 
set  in  the  smaller  sized  ty^^e  without  leading. 

The  order  of  the  chapters  follows  the  order  in  which  the  topics 
are  likely  to  be  taken  up  when  work  is  begun  in  the  fall  of  the  year. 
The  introductory  experiments  in  physics  and  chemistry  may  be 
omitted  until  the  study  of  the  seed  and  seedling,  thus  utilizing  the 
early  fall  days  for  the  work  on  the  flower,  insect  pollination,  and  the 
fruit.  The  subject  of  protoplasm  and  the  cell,  necessarily  somewhat 
vague  to  the  pupil,  must  be  taken  up  with  the  flower  in  order  that 
the  process  of  fertilization  may  be  understood.  The  study  of  the 
root,  stem,  and  leaf  follow  in  order,  emphasis  being  placed  through- 
out on  the  function  rather  than  structure.  The  chapter  on  plant 
ecology  is  so  placed  simply  for  convenience;  the  work  may  well 
come  in  connection  with  the  physiological  work  already  referred  to. 

Some  portion  of  the  work  outlined  on  the  cryptogams  is  not 
recommended  to  such  schools  as  have  no  laboratory  equipment,  the 
use  of  the  compound  microscope  being  essential  to  such  laboratory 


THE  PURPOSE  AND   PLAN   OF   THIS   BOOK  7 

exercises.  If  work  is  attempted  without  the  microscope,  the  mosses 
aud  ferns  present  the  best  points  for  attack ;  much  work  of  an 
economic  nature  may  also  be  done  with  the  yeasts,  molds,  and  bacte- 
ria. If  the  laboratory  equipment  permits,  several  days  should  be 
spent  in  the  laboratory  study  of  mucor  and  spirogyra,  the  latter 
being  used  to  teach  the  concept  of  the  cell. 

In  the  second  half  year  the  so-called  evolutionary  order  may  be 
followed  with  the  animal  types  studied.  It  is  desirable,  however,  to 
take  up  the  study  of  the  frog  in  the  early  spring  during  the  breeding 
season,  thus  leaving  the  study  of  insects  until  June,  when  insect  life 
is  more  abundant.  Human  physiology  may  be  begun  with  the  study 
of  the  frog  and  continued  for  the  rest  of  the  term^,  certain  lessons 
each  week  being  devoted  to  this  subject.  The  topics  of  foods,  diges- 
tion, assimilation,  blood  making,  and  circulation  may  well  be  taken 
up  in  connection  with  the  laboratory  work  outlined  on  the  frog ; 
breathing,  oxidations  in  the  body,  muscular  activity,  and  excretion 
come  well  with  the  treatment  of  the  insects. 

For  general  use  every  school  ought  to  have  at  least  one  compound 
microscope  for  demonstration  purposes.  For  low  power  demonstra- 
tion work  a  portable  microscope  such  as  is  manufactured  by  the 
Bausch  and  Lomb  Optical  Company  is  useful.  A  small  stock  of 
simple  reagents,  glassware,  and  other  apparatus,  as  noted  from  time 
to  time  in  the  following  pages,  are  also  necessary  parts  of  the  school 
equipment.  Excellent  results  may  be  obtained  with  little  or  no 
apparatus  except  that  made  by  the  pupils  and  teacher  working  to- 
gether. Let  no  one  feel  that  the  work  outlined  in  this  book  needs 
expensive  apparatus. 

Acknowledgments  are  due  to  Miss  A.  P.  Hazen  of  the  Wadleigh 
High  School  for  many  suggestions  and  for  her  careful  reading  of 
the  entire  manuscript.  The  manuscript  has  also  been  read  in  part 
by  Miss  M.  D.  Womack  of  the  Wadleigh  High  School,  H.  G.  Barber, 
C.  F.  Morse,  and  R.  W.  Sharpe  of  the  De  Witt  Clinton  High  School, 
and  Mr.  C.  W.  Beebe,  Curator  of  Birds,  New  York  Zoological  Park- 


8  THE  PURPOSE   AND  PLAN   OF   THIS   BOOK 

Proof  has  been  read  critically  by  three  of  my  former  pupils,  J.  W. 
Tietz,  P.  T.  Lacy,  and  J.  W.  Ingle.  To  all  of  the  above  my  thanks 
are  due« 

Thanks  are  due,  also,  to  Prof.  E.  B.  Wilson,  W.  C.  Stevens,  and 
C.  W.  Beebe,  Dr.  Alvin  Davison,  Dr.  Prank  Overton,  Mr.  Spencer, 
of  the  New  York  Aquarium,  the  United  States  Department 
of  Agriculture,  and  the  American  Museum  of  Natural  History, 
for  permission  to  copy  and  use  certain  cuts  and  photographs 
which  have  been  found  useful  in  teaching.  Prof.  G.  N.  Calkins 
of  Columbia  University  kindly  loaned  the  photograph  of  the 
Amoeba  reproduced  on  page  182.  E.  AY.  Coryell  and  J.  W.  Tietz 
made  several  of  the  photographs  of  experiments.  The  photograph 
of  the  humming  bird  was  used  by  permission  of  the  Polmer  and 
Schwing  Company,  Kochester,  N.Y.  In  particular  I  am  under 
obligation  to  my  former  coworker.  Dr.  C.  A.  King,  for  his  exam- 
ple of  earnest  and  inspiring  work,  to  Mr.  W.  P.  Hay,  Head  of  the 
Department  of  Biology  and  Chemistry,  in  the  Washington,  D.C., 
High  Schools,  for  his  helpful  criticisms,  and  to  Messrs.  Sedgwick 
and  Wilson,  whose  General  Biology  is  a  monumental  work  in  ele- 
mentary biological  teaching. 


CONTENTS 


PART  I.     BOTANY 


; 


CHAPTER 

I.  Introduction         ........ 

II.  Introduotohy  Experiments  in  Chemistry  and  Physics 

III.  Protoplasm  and  the  Cell 

IV.  Flowers         .... 
V.  Fruits  .         .        .         , 

VI.  Seeds  and  Seedlings  . 

VII.  Roots  and  their  Work 

VIII.  Buds  and  Stems   . 

IX.  Leaves  and  their  Functions 

X.  Ecology         .... 

XI.  Flowerless  Plants 


PAGE 

11 

15 

23 

31 

50 

66 

82 

98 

123 

142 

150 


PART  II.     ZOOLOGY 


XII.  Protozoa       .... 

XIII.  Metazoa         .        .        . 

XIV.  Sponges  .... 

XV.  CCELENTERATES 

XVI.  The  Starfish  and  its  Allies 

XVIL  Worms  ..... 

XVIII.  Crustaceans 

XIX.  Insects 

XX.  Spiders  and  Myriapods 

XXI.  MOLLUSKS 

XXII.  Fishes 

XXIII.  Amphibians  . 

XXIV.  Reptiles 
XXV,  Birds     .... 

XXVL  Mammals 

9 


179 
187 
191 
195 
203 
208 
215 
227 
256 
259 
271 
279 
286 
292 
308 


10 


CONTENTS 


PART  III.     HUMAN  PHYSIOLOGY 

CHAPTBB  PAGE 

XXVII.     Foods 317 

XXVIII.     Digestion  and  Absorption 330 

XXIX.     The  Blood 344 

XXX.       CiRCDLATION 350 

XXXI.     Muscles 362 

XXXII.     The  Skeleton ,         .  371 

XXXIII.  Respiration 380 

XXXIV.  Excretion 391 

XXXV.     The  Nervous  System 400 

XXXVI.     The  Senses 419 

Appendix 429 

Index  .,.ooe 431 


ELEMENTS   OF  BIOLOGY 


PART  I.    BOTANY 

I.     INTRODUCTION 

Science  and  Matter.  —  Science  deals  with  that  material  which 
occupies  all  the  space  around  us,  —  the  air,  the  water,  and  the 
earth.  This  material  is  called  matter.  Matter  is  the  building 
material  of  the  world  in  which  we  live. 

Matter  exists  in  this  world  in  two  distinct  states.  It  may  be 
living,  or  may  have  been  alive  at  some  previous  time,  in  which  case 
we  speak  of  it  as  organic  matter;  or  it  may  never  have  been  alive. 
The  latter  state  of  matter  is  called  inorganic.  Hence  we  find 
two  groups  of  sciences  which  deal  with  matter:  the  biological 
sciences,  which  treat  of  living  matter;  and  the  chemical  and 
physical  sciences,  which  deal  chiefly  with  inorganic  matter. 

Biology.  —  Biology  is  the  science  which  treats  of  matter  in  a 
living  state.  The  two  subdivisions  of  biology,  dealing  with  plant 
life  and  animal  life  respectively,  are  called  botany  and  zoology. 

Knowledge  in  Science  gained  by  Observation.  —  Science  has 
been  defined  as  "  knowledge  gained  by  exact  observation  and 
correct  thinking."  First  of  all,  science  is  a  kind  of  knowledge. 
It  is  accurate  knowledge.  But  it  is  possible  to  acquire  a  mass  of 
knowledge  not  scientific  with  the  sole  aid  of  a  text-book.  Such 
knowledge,  for  example,  might  be  that  of  the  Latin  or  the  German 
language.  Scientific  knowledge,  according  to  our  definition,  must 
be  gained  through  observation,  from  the  accurate  study  of  a  speci- 
men, something  that  we  may  see  and  touch.  It  is  not  enough  to 
study  a  book  alone;  this  may  be  an  aid,  but  the  specimen  is, 
after  all,  the  main  thing.  If  we  were  to  fit  ourselves  for  the  trade 
of  a  plumber  or  a  carpenter  or  a  mason,  we  certainly  should  not 
depend  upon  a  book  for  our  information  regarding  our  particular 

n.  C.  state  Collegt 


12  BOTANY 

trade.  We  should,  instead,  go  to  the  shop  and  there  learn  to 
work  with  the  tools  of  our  trade.  So,  in  the  pursuit  of  scientific 
work,  we  must  learn  to  use  the  tools  with  which  nature  has  pro- 
vided us,  —  our  hands,  our  eyes,  and  the  thinking  mechanism,  our 
brains.  As  Louis  Agassiz,  the  famous  naturalist  said,  "  Study 
nature,  not  books." 

Classification  of  Facts  Observed.  —  The  knowledge  we  gain  by 
observation  is  worth  very  little  to  us  or  to  any  one  else  unless  we 
use  our  brains  to  classify  it  and  to  apply  it.  We  must  find  out 
what  different  facts  mean  as  related  to  one  another. 

Single  isolated  facts  about  the  color,  coats,  or  markings  found 
on  the  coats  of  a  kidney  bean  mean  but  little  to  us  if  we  cannot 
correlate  these  observ^ations  w^ith  others  and  relate  them  to  scien- 
tific truths  already  learned.  A  great  many  men,  working  for  long 
periods  of  time,  have  gathered  together  a  large  number  of  single 
isolated  facts,  have  correlated  these  facts,  and  then  have  given  to 
the  world  discoveries  of  world-wide  importance.  A  careful  boy 
or  girl  may,  by  his  own  painstaking  work  in  science,  find  out 
some  fact  that  is  new,  and  in  a  small  way  make  a  discovery.  It 
is  one  of  the  most  interesting  things  about  science  work,  that  it 
has  in  it  the  spirit  of  discovery. 

Morphology.  —  It  is  evident  that,  in  order  to  understand  the  cause 
of  the  regular  movements  of  a  clock,  it  would  be  necessary  to  take 
the  wheels  apart  and  to  find  out  the  structure  of  the  different 
pieces  composing  the  works,  so  as  to  see  how  these  parts  are  re- 
lated to  each  other.  In  the  study  of  biology  it  is  usually  found 
best  to  begin  with  the  study  of  the  form  and  structure  of  the 
parts  of  an  organism;   this  study  is  called  morphology. 

Physiology.  —  After  we  have  discovered  in  the  clock  the  form 
and  structure  of  the  different  wheels  and  cogs  and  the  relation  of 
one  to  the  other,  we  are  in  a  position  to  put  them  together  again 
and  to  find  out  how  they  move  and  what  causes  the  movement: 
to  study  the  use  or  function  of  each  part.  The  study  of  the  uses 
or  functions  of  the  parts  of  an  organism  is  called  physiology. 

The  Experiment.  —  In  order  to  study  physiology,  and  indeed 
most  sciences,  we  frequently  have  to  make  use  of  an  experiment. 
There  are  always  three  steps  in  a  complete  experiment.     Beginners 


INTRODUCTION  13 

in  scientific  study  should  always  try  to  follow  these  steps  exactly. 
First  comes  actually  making  the  experiment.  This  includes  col- 
lecting and  putting  together  such  materials  as  we  may  need,  a 
statement  of  the  work  we  perform,  and  most  important  of  all,  a 
definite  statement  of  the  problem  that  we  are  attempting  to 
solve.  The  second  step  is  to  make  observations  on  the  experiment 
which  we  have  set  up.  These  observations  may  extend  over  a 
period  of  several  days  or  even  weeks.  They  must  be  noted  in 
such  form  that  we  can  use  them  in  the  third  step  of  the  experiment. 
This  step,  the  hardest  of  all,  consists  in  drawing  conclusions  from 
the  observations  we  have  previously  made.  Every  experiment 
should  be  illustrated  with  drawings  to  show  all  the  apparatus 
used  at  each  stage  of  the  process. 

Use  of  Notebook.  —  Scientific  work  should  be  carefully  and  accurately- 
performed,  and  the  results  should  be  recorded  in  some  permanent  form. 
For  this  purpose  a  notebook  is  used,  in  which  the  student  makes  a  complete 
record,  not  only  of  experiments  but  also  of  all  other  work  performed  in  the 
schoolroom,  outdoors  or  at  home.  The  notebook  best  adapted  to  this 
purpose  is  one  in  which  the  leaves  may  be  added  from  time  to  time.  For 
work  done  outdoors,  field  trips  and  the  like,  it  is  better  to  have  a  separate 
notebook.  This  may  be  used  as  a  working  book,  in  which  observations  are 
jotted  down  in  a  brief  form  and  later  copied  in  ink  in  the  laboratory  note- 
book.    It  is  of  advantage  to  have  all  your  notes  under  one  cover. 

Drawing.  —  Drawing  constitutes  a  very  important  part  of  your  labora- 
tory work.  In  scientific  drawing,  every  line  made  should  mean  something; 
the  lines  should  be  firm  and  bold;  sketchy  work  should  noi  be  allowed.  A 
hard  (HHHHH)  pencil  should  be  used.  If  you  are  expert  with  the  draw- 
ing pen,  then  make  your  drawings  in  ink.  Do  not  attempt  to  shade  your 
drawing.  Every  part  of  the  drawing  to  which  you  wish  to  call  attention 
must  be  carefully  labeled.  Place  a  neat  index  of  the  parts  so  labeled 
directly  underneath  the  drawing,  near  the  bottom  of  the  page.  Only  one 
side  of  the  paper  should  be  used  in  any  scientific  work,  whether  written 

work  or  drawings. 

The  Laboratory.  —  For  convenience,  science  work  is  usually  performed 
in  a  room  called  a  laboratory.  This  room  may  be  fitted  up  with  certain 
appliances  to  make  the  work  easier.  But  in  biology  the  great  out  of  doors 
makes  a  much  more  useful  laboratory  than  any  schoolroom.  However, 
observations  made  at  home  or  out  of  doors  should,  when  possible,  be  veri- 
fied in  the  laboratory  under  the  supervision  of  a  teacher. 

Frequently  the  laboratory  differs  little  if  at  all  from  an  ordinary  school- 
room.    It  should  always  be  well  lighted  and,  if  possible,  should  have  north 


14  BOTANY 

light  as  well  as  some  direct  sunlight.  A  corner  room  is  best  if  it  can  be  ob- 
tained. If  tables  are  used,  they  should  be  arranged  so  that  each  student 
may  get  as  much  light  as  possible  without  shading  his  neighbor. 

Instruments  used.  —  Every  pupil  ought  to  provide  himself,  in  addition 
to  the  laboratory  notebook  and  a  hard  pencil,  with  the  following  articles :  a 
hand  lens  (a  small  brass-mounted  tripod  lens,  one  mounted  in  vulcanite,  or 
the  small  lens  known  as  a  linen  tester),  two  or  three  darning  needles  mounted 
in  elder  pith  or  in  wooden  handles,  a  good  eraser,  and  a  ruler  marked  with 
the  metric  system.  A  small  pair  of  forceps,  scissors,  and  a  light,  thin- 
bladed  knife  or  scalpel  are  useful,  but  not  essential  for  most  laboratory 
work. 

Interest  in  Laboratory  Work  Essential.  —  It  is  not,  however,  the 
laboratory  or  the  equipment  that  makes  the  laboratory  work  a  success. 
It  is  rather  the  spirit  of  the  pupils.  Interest  in  the  work  is  the  first  essential. 
When  at  work  on  what  may  seem  to  be  only  dry  details,  look  ahead  and 
think  about  what  you  are  doing.  Try  to  find  a  purpose  in  everything  that 
you  do.  It  is  possible  to  make  any  piece  of  biological  work  interesting  by 
keeping  in  mind  that  everything  in  nature  is  part  of  a  great  plan  and  has 
a  purpose.  It  is  your  place  to  find  out  just  how  the  given  part  that  you 
may  be  studying  is  fitted  or  adapted  to  its  work  in  the  general  plan. 

At  the  end  of  each  of  the  following  chapters  is  a  list  of  books  which  have  proved 
their  use  either  as  reference  reading  for  students  or  as  aids  to  the  teacher.  Most 
of  the  books  mentioned  are  within  the  means  of  the  small  school.  Two  sets  are 
expensive :  one,  The  Natural  History  of  Plants,  by  Kerner,  translated  by  Oliver, 
published  by  Henry  Holt  and  Company,  in  two  volumes,  at  Sll ;  the  other.  Plant 
Geography  upon  a  Physiological  Basis,  by  Schimper,  published  by  the  Clarendon 
Press,  $12 ;  but  both  works  are  invaluable  for  reference. 

Two  books  stand  out  from  the  pedagogical  standpoint  as  by  far  the  most  helpful 
of  their  kind  on  the  market.  No  teacher  of  botany  or  zodlogy  can  afford  to  be 
without  them.  They  are  :  Lloyd  and  Bigelow,  The  Teaching  of  Biology,  Long- 
mans, Green,  and  Company,  and  C.  F.  Hodge,  Nature  Study  and  Life,  Ginn  and 
Company.  Other  books  of  great  value  from  the  teacher's  standpoint  are  :  Ganong, 
The  Teaching  Botanist,  The  Macmillan  Company;  L.  H.  Bailey,  The  Nature  Study 
Idea,  Doubleday,  Page,  and  Company;  and  C.  B.  Scott,  Nature  Study  and  the 
Child,  D.  C.  Heath  and  Company. 


II.     INTRODUCTORY  EXPERIMENTS  IN  CHEMISTRY 

AND   PHYSICS 

In  the  introductory  chapter  we  learned  that  science  concerns 
itself  with  matter,  and  that  the  science  of  biology  is  concerned 
with  the  study  of  this  matter  when  it  is  in  a  living  state.  In 
order  to  understand  this  definition  we  must  first  get  a  conception 
of  what  matter  really  is. 

Matter.  —  If  you  take  a  piece  of  ice  in  your  hand,  you  are  aware 
that  it  is  cold,  and  that  it  has  weight  and  a  certain  form.  We 
call  it  a  solid.  A  few  minutes'  exposure  to  the  warmth  of  your 
hand  will  change  this  solid  into  a  liquid.  If  the  water  thus 
formed  be  heated  over  a  flame  until  it  boils,  it  may  be  changed 
again,  this  time  into  a  gas  which  passes  off  into  the  air  and  be- 
comes invisible.  The  ice  has  successively  changed  from  a  solid 
to  a  liquid  and  then  to  a  gas.  In  each  state  we  could  measure 
it  and  weigh  it.  In  each  form  it  occupies  space.  It  must  be 
considered  matter,  whether  in  the  form  of  a  solid,  a  liquid,  or  a 
gas. 

Physics  and  Chemistry.  —  The  sciences  which  treat  chiefly  of  the 
properties  and  forces  of  inorganic  or  dead  matter,  and  of  the  rela- 
tions of  the  parts  of  the  substances  composing  it,  are  known  as 
the  sciences  of  physics  and  chemistry. 

Chemical  Element.  —  All  the  building  materials  of  this  uni- 
verse, both  living  and  lifeless,  are  classified  by  chemists  as  either 
chemical  elements  or  chemical  compounds.  A  chemical  element  is  so 
simple  in  its  structure  that  it  cannot  be  broken  or  decomposed 
into  a  simpler  substance.  Examples  of  such  substances  are  oxy- 
gen, making  up  about  one  fifth  of  the  atmosphere;  nitrogen,  com- 
posing nearly  all  the  remainder  of  pure  air;  carbon,  an  element 
that  enters  into  the  composition  of  all  organic  living  things  or 
those  that  once  possessed  life;  and  over  sixty  others  of  more 
or  less  importance  to  us  in  the  study  of  biology. 

16 


16  BOTANY 

Preparation  of  Oxygen,  —  Oxygen  may  be  easily  prepared  in  the  school- 
room or  at  home   in  the  following  manner .1      Heat  half  a  teaspoonful  of 

black  oxide  of  manganese  with  a  little  more  than  its  bulk 
of  chlorate  of  potash  in  a  test  tube  over  a  bunsen  flame 
or  a  spirit  lamp.  Vapors  will  be  seen  to  arise  as  the  mix- 
ture becomes  heated.  After  a  moment  insert  a  glowing 
match  into  the  mouth  of  the  test  tube;  it  bursts  into  a 
blight  flame.  In  what  form  does  oxygen  pass  off  from 
the  two  chemicals  in  the  test  tube?  How  could  you 
determine  the  presence  of  oxygen  in  a  substance?  Is 
there  oxygen  in  the  air?    How  do  you  know? 

Properties  of  Oxygen. — The  physical  proper- 
ties of  oxygen  are  those  which  we  determine  with 
Preparing  oxygen,    our  senses.     Oxygen,  when  carefully  prepared,  is 

found  to  be  a  colorless,  odorless,  and  tasteless  gas. 
It  is  known  to  form  nearly  one  half  of  the  earth's  surface,  to  form 
eight  ninths  of  all  water  and  over  three  fourths  of  the  weight  of  the 
plants  and  animals  inhabiting  this  world  of  ours.  It  has  the  very 
important  chemical  property  of  causing  things  placed  in  it  to  burn. 
If,  for  example,  a  piece  of  picture  wire  is  heated  red-hot, and  then 
placed  in  a  jar  of  oxygen,  the  metal  will  burn  with  a  bright  flame. 

Oxidation.  —  Light  carefully  a  small  piece  of  magnesium  wire  and  then 
place  it  in  a  test  tube  in  which  you  have  previously  made  oxygen.  Notice 
the  very  brilliant  flame.  A  light-colored  ash  remains.  This  is  magnesium 
oxide.  In  the  above  experiment  the  oxygen  in  the  test  tube  unites  with 
the  magnesium  so  rapidly  as  to  form  a  flame.  This  process  is  known  as  a 
combustion. 

The  chemical  union  of  oxygen  with  any  other  substance  is  called 
oxidation.  Can  you  distinguish  between  combustion  and  oxida- 
tion? Oxidation  takes  place  wherever  oxygen  is  present.  These 
facts,  as  we  shall  see  later,  have  a  far-reaching  significance  in  the 
understanding  of  some  of  the  most  important  problems  of  biology. 

Oxidation  in  a  Match. — The  simple  process  of  striking  a  sulphur  match 
gives  us  another  illustration  of  this  process  of  oxidation.  The  head  of  the 
match  is  formed  of  a  composition  of  phosphorus,  sulphur,  and  some  other 
materials.  Phosphorus  is  a  chemical  element  distinguished  by  its  extreme 
inflammability.  It  unites  with  oxygen  at  a  comparatively  low  temperature. 
Sulphur  is  another  chemical  element  that  combines  somewhat  easily  with 
oxygen  but  at  a  much  higher  temperature.  The  rest  of  the  match  head 
is  made  up  of  red  lead,  niter  or  some  other  substance  that  will  release  oxy- 
gen,  and  some  glue  or  gum  to  bind  the  materials  together.     The  heat 

*  For  a  conci.se  statement  of  this  and  following  experiments  in  the  scientific  form 
expected  from  the  pupil,  see  Hunter  and  Valentine,  Laboratory  Maniud  of  Biology, 
Henry  Holt  and  Company,  pages  213  ff. 


EXPERIMENTS   IN   CHEMISTRY  AND  PHYSICS     17 

caused  by  the  friction  of  the  match  head  against  the  striking  surface  is 
enough  to  cause  the  phosphorus  to  ignite;  this  in  turn  ignites  the  sulphur 
and  finally  the  wood  of  the  match,  composed  largely  of  the  element  carbon, 
is  lighted  and  oxidized.  If  we  could  take  out  the  different  chemical  ele- 
ments of  which  the  match  is  formed  and  oxidize  them  separately  we  should 
find  that  the  amount  of  heat  needed  to  start  the  oxidation  of  the 
substances  would  vary  greatl3\  The  element  phosphorus,  for  ex- 
ample, is  kept  under  water  in  a  glass  jar  because  of  the  extreme 
readiness  with  which  it  unites  with  oxygen. 

Experiment.  —  Oxidation  may  take  place  with  very  little  heat 
present,  although  heat  is  always  a  result  of  oxidation. 

Place  an  iron  nail  in  a  bottle  of  water,  and  cork  and  seal  the  bottle. 
Place  another  nail  in  a  saucer  in  which 
is  kept  a  little  water.  Note  the  for- 
mation of  rust  on  the  nail  in  the 
saucer  and  the  absence  of  rust  on  the 
nail  in  the  bottle.  Rust  is  iron  oxide 
and  is  formed  by  the  union  of  iron 
and  oxygen.  This  kind  of  oxidation 
is  said  to  be  o,  slow  oxidation.  Slow 
oxidations  are  constantly  taking  place 
in  nature  and  result  in  the  process  of 
decay  and  breaking  down  of  complex 
materials  into  simpler  materials. 


Oxyqen  in  the  air 
^ 


3 


Diagram  of  combustion  or  rapid  oxida- 
tion in  a  stove. 


Heat  given  off  as  result  of  Oxidaticn.  —  One  of  the  most  im- 
portant effects  of  oxidation  lies  in  the  fact  that,  when  anything  is 
oxidized, heat  is  produced.  This  heat  maybe  of  the  greatest  use. 
Coal,  when  oxidized,  gives  off  heat;  this  heat  boils  the  water  in 
the  tubes  of  a  boiler;  steam  is  generated,  wheels  of  an  engine 
turn,  and  work  is  performed.  The  energy  released  by  the  burning 
of  coal  may  be  transformed  into  any  kind  of  work  power.  Energy 
is  the  ability  to  perform  work. 

Carbon.  —  Another  chemical  element  of  much  importance  to 
us  is  carbon.  This  element  makes  up  an  important  part  of  all 
things  that  now  have  or  at  any  time  had  life.  Such  matter  we 
call  organic.  Carbon  is  found  making  up  part  of  the  bodies  of 
plants  and  animals,  of  coal,  and  in  a  nearly  pure  state  in  the 
diamond.  The  presence  of  carbon  can  often  be  detected  by  the 
fact  that  the  substance  containing  it  turns  black  upon  being 
heated  in  a  flame. 


Experiment.  —  Heat  separately  on  a  tin  plate  some  leaves,  sticks  of  wood, 
gravel,  sand,  and  rich  black  earth.  Place  them  over  a  hot  flame  for  some 
minutes      Which  of  the  above  materials  contains  carbon? 

If  some  substance  that  contains  carbon,  as  a  piece  of  wood,  is  burned  in  a 
jar  with  a  tight-fitting  cover,  the  flame  will  be  seen  to  go  out  after  a  short 

hunter's  BIOL. — 2 


18 


BOTANY 


^ 


h 


time.  This  will  occur  before  all  the  wood  is  consumed.  Another  splinter 
of  wood,  placed  in  a  jar  with  the  cover  off,  will  burn  slowly  but  completely. 
A  third  piece  of  wood  burned  in  the  air  will  be  quickly  and  completely 
consumed.  If  now  a  little  limewater^  is  poured  into  the  jar  which  was 
closed,  and  the  contents  shaken  up,  the  limewater  will  be  found  to  turn  a 
milky  color.     This  milky  appearance  is  due  to  the  formation  within  the  jar 

of  a  material  known  as  calcium  carbonate.  This 
is  thrown  down  in  the  liquid  as  a  result  of  the 
union  of  carbon  with  lime.  Evidently  some  of 
the  carbon  from  the  wood  has  passed  in  the  form 
of  a  gas  into  the  limewater  and  there  united  with 
the  calcium  in  the  lime.  Remembering  what  we 
know  about  oxidation,  we  see  that  the  carbon  of 
the  wood  has  passed  ofif  and  united  with  oxygen 
of  the  air  in  the  jar.  Thus,  by  the  uniting  of  the 
two  chemical  elements,  a  chemical  compound  has 
heenformed.  The  presence  of  carbon  dioxide  is 
known  by  the  fact  that  it  puts  out  a  flame  and 
that  it  turns  limewater  milky.  This  compound 
is  known  to  chemists  as  carbon  dioxide.^ 

Nitrogen.  —  There  is  another  gaseous 
substance  that  will  not  support  combus- 
tion; this  is  the  element  nitrogen.  Its 
presence  in  the  atmosphere  is  shown  by 
the  following  experiment:  — 

Invert  a  bell  jar  in  a  large,  deep  dish  of  water, 
having  previously  placed  within  the  jar  on  the 
surface  of  the  water  a  piece  of  phosphorus  sup- 
ported on  a  flat  bit  of  wood  or  cork.  Leave  the 
experiment  for  at  least  two  days  undisturbed  (or, 
the  phosphorus  may  be  lighted  and  then  the  jar 
left  for  a  few  hours  untouched).  After  that  time  the  water  will  be  found 
to  have  risen  considerably  in  the  jar.^     If  you  make  a  mark  on  the  cover 

*  Limewater  can  be  made  by  shaking  up  a  piece  of  quicklime  the  size  of  your  fist 
in  about  two  quarts  of  water.  Filter  or  strain  the  limewater  into  bottles  and  it 
is  ready  for  use. 

2  Chemists  have  shown  that  any  given  structure  is  made  up  of  molecules.  A 
molecule  is  the  smallest  bit  of  matter  that  can  exist  separately  and  still  retain  its 
composition  and  properties.  A  molecule  is  composed  of  still  smaller  particles 
called  atoms.  Carbon  dioxide  is  so  called  because  its  molecule  is  made  up  of  one 
atom  of  carbon  and  two  atoms  of  oxygen.  It  is  customary  to  use  certain  letters 
or  symbols  to  designate  certain  chemical  elements,  as  C  for  carbon,  H  for  hydrogen, 
N  for  nitrogen.  P  for  phosphorus,  Fe  (Latin  ferrum)  for  iron.  The  molecule  of 
carbon  dioxide  is  made  of  one  part  of  carbon  and  two  of  oxygen ;  it  is  written  CO2. 
This  is  called  the  chemical  formula.  If  an  electric  current  is  passed  through  a  jar 
of  water,  the  contents  will  be  broken  down  into  the  elements  hydrogen  and  oxygen. 
If  now  the  gases  are  carefully  collected,  there  will  be  found  to  be  exactly  twice  as 
much  of  the  hydrogen  gas  as  there  is  of  the  oxygen.  The  chemical  formula  for 
water  is  H2O.     See  figure. 

^  It  would  be  well  for  the  teacher  at  this  place  to  bring  up.the  subject  of  atrnos- 
pheric  pressure.  Air  presses  down  on  the  earth's  surface  at  sea  level  with  a  weight 
of  fifteen  pounds  to  every  square  inch  of  surface. 


Apparatus  for  separating 
water  into  the  two  ele- 
ments hydrogen  and 
oxygen. 


EXPERIMENTS   IN   CHEMISTRY  AND   PHYSICS     19 


r 

to  show  where  the  water  stood,  you  may  measure  the  space  occupied  by 
the  water  in  the  jar.  This  space  will  be  found  to  be  almost  exactly  one  fifth 
of  the  cubic  contents  of  the  jar.  It  was 
occupied  by  the  oxygen  of  the  air,  this  hav- 
ing been  used  up  by  the  oxidation  of  the 
phosphorus.  The  remaining  space  at  the 
completion  of  the  experiment  is  occupied  by 
the  nitrogen,  which  makes  the  remaining 
four  fifths  of  the  atmosphere. 

The  physical  properties  of  nitrogen 
are  its  lack  of  color,  taste,  and  odor. 
Its  chief  chemical  characteristics  are 

its  inability  to  support  combustion  and     ^^|.^^^^.-     .  :-v     ^^   ) 
its  slight  affinity  for  other  substances.  " 


Experiment  to  show  the  amount 
of  nitrogen  present  in  the  air. 


Mineral  Matter  in  Living  Things. — 
We  saw  in  the  experiment  for  the  detection 
of  carbon  by  burning,  that  the  sand  or  gravel  contained  no  carbon.  If  a  piece 
of  wood  is  burned  in  a  very  hot  fire,  the  carbon  in  it  will  all  be  consumed, 
and  eventually  nothing  will  be  left  except  a  grayish  ash.  This  ash  is  well 
seen  after  a  wood  fire  in  the  fireplace,  or  after  a  bonfire  of  dry  leaves. 
This  ash  consists  entirely  of  mineral  matter  which  the  plant  has  taken  up 
from  the  soil,  dissolved  in  water,  and  which  has  been  stored  in  the  wood 
or  leaves. 

If  we  were  able  by  careful  analysis  to  reduce  a  plant  and  an  animal 
to  the  chemical  compounds  of  which  they  were  formed,  we  should  discover 
that  both  contained  mineral  or  inorganic  material.  We  have  just  seen 
examples  of  this  in  plants.  Mineral  matter  is  found  in  bone,  in  the  shells 
covering  mollusks,  and  in  many  of  the  other  parts  of  the  bodies  of  animals. 

Water  in  Living  Things.  —  Water  forms  an  important  part  of  the  sub- 
stance of  plants  and  animals.  This  can  easily  be  proved  by  weighing  a 
number  of  green  leaves,  placing  them  in  a  hot  oven  for  a  few  moments,  and 
then  reweighing.  How  much  weight  of  a  given  quantity  of  leaves  is  made 
up  of  water?  Make  the  same  experiment  with  some  soft-bodied  ani- 
mal, as  an  oyster  removed  from  the  shell.  Some  jellyfish  are  composed 
of  over  90  per  cent  water.  The  human  body  contains  60  per  cent 
water. 

Gases  Present.  —  Some  gases  are  found  in  a  free  state  in  the  bodies  of 
plants  or  animals.  Oxygen  is  of  course  present  wherever  oxidation  is 
taking  place,  as  is  carbon  dioxide.  Other  gases  may  be  present  in  minute 
quantities. 

Classification  of  Organic  Matter.  —  The  organic  or  living  part 
of  a  plant  or  animal  is  made  up  largely  of  the  elements  carbon, 
hydrogen,  oxygen,  and  nitrogen,  with  a  very  minute  amount  of 


20  BOTANY 

several  other  elements,  which  collectively  we  may  call  mineral 
matters.  If  we  were  to  separate  a  plant  or  animal  chemically 
into  various  organic  compounds,  we  should  find  it  composed  of 
various  groups  of  tissues,  the  chemical  compositions  of  which  are 
more  or  less  alike.  For  example,  the  living  part  of  a  plant 
corresponds  chemically  with  the  living  part  of  an  animal.  The 
starch  found  in  grains  or  roots  of  plants  has  nearly  the  same 
chemical  formula  as  the  animal  starch  found  in  the  liver  of  man; 
the  oils  of  a  nut  or  fruit  are  of  composition  closely  allied  to  the 
fat  in  the  body,  or  in  a  sheep  or  cow.  These  building  materials 
of  a  plant  or  animal  may  be  placed  in  one  of  the  three  following 
groups  of  organic  substances:  carbohydrates,  materials  containing 
a  certain  proportion  of  carbon,  hydrogen,  and  oxygen;  organic 
fats  and  oils,  which  contain  chiefly  hydrogen  and  carbon;  and 
nitrogenous,  or  'proteid  substances,  which  contain  nitrogen  in  addi- 
tion to  the  above-mentioned  elements.  The  above  three  kinds  of 
organic  materials  also  form  the  organic  foods  of  all  animals  and 
plants. 

Foods.  —  What  is  a  food  ?  We  know  that  if  we  eat  a  certain 
amount  of  proper  foods  at  regular  times,  we  shall  go  on  doing  a 
certain  amount  of  work,  both  manual  and  mental.  We  know, 
too,  that  day  by  day,  if  our  general  health  is  good,  we  are  adding 
weight  to  our  body,  and  that  added  weight  comes  as  the  result 
of  taking  food  into  the  body.  What  is  true  of  a  boy  or  girl  is 
equally  true  of  plants.  If  food  is  supplied  in  proper  quantity 
and  proportion,  they  will  live  and  grow;  if  the  food  supply  is 
cut  off,  or  even  greatly  reduced,  they  will  suffer  and  may  die. 
From  this,  the  definition  which  follows  is  evident. 

A  food  is  a  substance  that  forms  the  material  for  the  growth  or 
repair  of  the  body  of  a  plant  or  animal  or  that  furnishes  energy 
for  it. 

Nutrients.  —  Food  substances  may  be  classed  into  a  number  of 
groups,  each  of  Avhich  may  be  detected  by  means  of  its  chemical 
composition.  Such  food  substances  are  known  as  nutrients.  Let 
us  now  examine  a  few  of  the  nutrients  that  we  are  likely  to  meet 
in  our  daily  life,  and  see  how  we  could  test  chemically  for  their 
presence. 


EXPERIMENTS   IN   CHEMISTRY   AND   PHYSICS      21 

Carbohydrates.  —  Starch  and  sugar  ^  are  common  examples  of 
this  group  of  substances. 

Starch  Test.  —  If  the  substance  to  be  tested  is  a  solid,  break  or  crush  it 
and  add  water  to  it.  Pour  over  it  a  few  drops  of  iodine  solution  diluted 
with  water. 2  Notice  the  color  of  the  iodine,  a  dark  brown;  after  it  has 
touched  the  material  supposed  to  contain  starch,  note  any  change  in  color. 
If  starch  is  present,  it  will  turn  dark  blue. 

Grape  Sugar.  —  There  are  several  forms  of  sugar  commonly 
used  as  food ;  for  example,  cane  sugar,  beet  sugar,  and  grape  sugar, 
the  latter  commonly  known  as  glucose.  Glucose,  or  grape  sugar,  is 
manufactured  commercially  by  pouring  sulphuric  acid  over  starch. 
It  is  used  as  an  adulterant  for  many  kinds  of  foods,  especially 
in  sirups,  honey,  and  candy. 

Test  for  Grape  Sugar.  —  The  presence  of  grape  sugar  is  determined  by 
the  following  test :  Place  in  a  test  tube  the  substance  to  be  tested  and  heat 
it  in  a  little  water  so  as  to  dissolve  the  sugar.  Add  to  the  fluid  twice  its 
bulk  of  Fehling's  solution,-''  which  has  been  previously  prepared.  Heat 
the  mixture,  which  should  now  have  a  blue  color,  in  the  test  tube.  If  grape 
sugar  is  present  in  considerable  quantity,  the  contents  of  the  tube  will  turn 
first  a  greenish,  then  yellow,  and  finally  a  brick-red  color.  Smaller  amounts 
will  show  less  decided  red.  This  change  also  appears  if  Fehling's  solution 
is  boiled  with  cane  sugar.  A  more  accurate  test  is  obtained  by  placing  the 
substance  believed  to  contain  grape  sugar  in  a  test  tube  containing  Fehling's 
solution  and  allowing  the  mixture  to  remain  over  night  in  a  moderately 
warm  room.  If  grape  sugar  is  present,  a  red  deposit  or  precipitate  (copper 
oxide)  will  be  found  in  the  tube  the  next  morning. 

Organic  Fats  and  Oils.  —  Tests  for  fats :  Rub  the  material  believed  to 
contain  oil  several  times  on  paper  and  hold  the  paper  to  the  light.  If  oil 
is  present,  the  paper  will  show  a  translucent  grease  spot.  Try  this  with 
several  different  nuts  and  decide  which  has  the  most  oil. 

A  second  test  for  oil  is  as  follows:  Heat  the  substance  to  be  tested  in  an 
oven  on  a  piece  of  paper.     If  oil  is  present,  the  paper  will  show  a  grease  spot. 

Third  test :  Reduce  the  substance  to  small  pieces  and  pour  benzine,  ether, 
or  other  volatile  oil  over  it.  Allow  the  benzine  or  ether  to  evaporate;  the 
oil  that  remains  is  the  extracted  oil  from  the  substance  tested. 

1  The  chemical  formula  for  starch  is  CgHiqOs  ;    that  of  grape  sugar,  CoHioOe. 

2  Iodine  solution  is  made  by  simply  adding  a  few  crystals  of  the  element  iodine 
to  95  per  cent  alcohol ;  or,  better,  take  by  weight  1  gram  of  iodine  crystals,  f  gram 
of  iodide  of  potassiimi,  and  dilute  to  a  dark  brown  color  in  weak  alcohol  (35  per  cent) 
or  distilled  water. 

3  To  make  Fehhng's  solution  (so  called  after  its  discoverer),  add  to  35  grams  of 
copper  sulphate  (blue  vitriol)  500  cubic  centimeters  of  water.  Put  aside  until  it  is 
completely  dissolved.     Call  this  solution  No.  1.  j  u- 

To  160  grams  of  caustic  soda  and  173  fframs  of  Rochelle  salt  add  500  cub\c 
centimeters  of  water.     Dilute  to  1  liter.    Call  this  solution  No.  2. 
For  use  mix  equal  parts  of  solution  1  and  2. 
The  following  formula  is  also  convenient :  — 

I.    Copper  Sulphate  :   9  grams  in  250  c.c.  water. 
IT.     Sodium  Hydroxide  :   30  grams  in  250  c.c.  water. 
III.    Rochelle  Salt :  43  grams  in  250  c.c.  water. 
For  use  add  to  equal  parts  I,  II,  and  III,  two  parts  of  water. 


22  BOTANY 

Proteids.  —  Nitrogenous  foods,  or  proteids,  contain  the  element 
nitrogen  in  addition  to  carbon,  h3'drogen,  and  oxygen  of  the  car- 
bohydrates and  hydrocarbons.  They  include  some  of  the  most  com- 
plex substances  known  to  the  chemist,  and  as  we  shall  see,  have  a 
chemical  composition  very  near  to  that  of  living  matter.  Proteids 
occur  in  several  different  forms,  but  the  following  tests  will  cover 
most  cases  commonly  met.  White  of  egg,  lean  meat,  beans,  and  peas 
are  examples  of  substances  composed  in  a  large  part  of  proteid. 

Place  in  a  test  tube  the  substance  to  be  tested;  for  example,  a  bit  of  hard- 
boiled  egg.  Pour  over  it  a  little  strong  (80  per  cent)  nitric  acid.  Note  the 
color  that  appears  —  a  lemon  yellow.  Now  wash  the  egg  in  water  and  add  a 
little  ammonium  hydrate.  The  color  now  changes  to  a  deep  orange,  show- 
ing that  a  proteid  is  present. 

If  the  proteid  is  in  a  liquid  state,  its  presence  may  be  proved  by  heating ;  if 
it  coagulates  or  thickens,  as  does  the  white  of  an  egg,  when  boiled,  then 
proteid  in  the  form  of  an  albumen  is  present. 

Another  characteristic  proteid  test  easily  made  at  home  is  by  burning 
the  substance.  If  it  burns  with  the  odor  of  burning  feathers  or  leather, 
then  proteid  forms  part  of  its  composition. 

Books  for  Reference 
for  the  pupil 

Avery-Sinnott,  First  Lessons  in  Physical  Science.     American  Book  Company. 
Eddy,  Experimental  Physiology  and  Anatomy.     American  Book  Company. 
Hunter  and  Valentine,  Laboratory  Manual  of  Biology.     Henry  Holt  and  Company. 
Peabody,  Laboratory  Exercises  in  Anatomy  and  Physiology.     Henry  Holt  and  Com- 
pany. 

FOR   THE   TEACHER 

Foster,  A  Text-hook  of  Physiology.     The  Macmillan  Company. 

Green,  Vegetable  Physiology.     J.  and  A.  Churchill. 

Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 


III.     PROTOPLASM   AND   THE  CELL 


A  Living  Plant.  —  If  we  walk  out  any  afternoon  in  the  fall  of 
the  year,  we  notice  the  many  forms  of  plant  life  that  fill  the  waste 
places  along  the  waysides 
and  make  their  way  into 
the  cultivated  gardens 
and  fields,  driving  out 
the  rightful  inhabitants. 
We  call  such  plants 
weeds.  Let  us  study 
some  common  weed  such 
as  the  yellow-blossomed 
butter  and  eggs  or  the 
ubiquitous  shepherd's 
purse,  with  the  intention 
of  finding  out  how  such 
plants  are  so  well  fitted 
to  live.  If  we  think  of  the 
plant  as  a  mass  of  living 
matter,  we  at  once  are 
struck  with  the  evident 
fact  that  the  living  ma- 
terial has  taken  on  very 
different  forms  in  dif- 
ferent parts  of  the  plant. ^ 
The  root  below  the  sur- 
face of  the  ground  dif- 
fers considerably  in  form 
from  the  stem,  which  in  turn  differs  in  structure  from  the  leaves. 

^  The  living  matter  of  the  plants  is  covered  by  dead  organic  matter  formed  by  the 
activity  of  the  live  part.  Thus  the  soft  living  mass  within  may  be  molded  into 
various  shapes,  as  stem,  root,  or  leaves,  with  the  help  of  the  strong  and  rigid  dead 
parts  of  the  plant. 

23 


Shepherd's  purse;  F^  flowers;  F,  fruits;  5,  stem; 
L,  leaves;  R,  roots. 


24 


BOTANY 


Functions  of  the  Parts  of  a  Plant.  —  Still  more  prominent  are 
the  structures  we  call  flowers  and  fruits.  Each  of  these  structures 
differs  from  each  other  part,  and  each  has  a  different  work  or 
function  to  perform  for  the  plant.  The  root  holds  the  plant  firmly 
in  the  ground  and  takes  in  water;  the  stem  holds  the  leaves  up  to  the 
light;  the  leaves,  under  certain  conditions,  manufacture  food  for  the 
plant;  the  flowers  form  the  fruits;  the  fruits  hold  the  seeds,  which  in 
turn  reproduce  young  plants  of  the  same  kind. 

Organs. —  Each  part  of  a  plant  or  animal,  having  a  separate  work  or 
function,is  known  as  an  organ.  Most  plants  and  animals  are  composed 

of  organs;  hence  any  hving  thing, 
even  the  simplest  single  living  cell, 
has  come  to  be  called  an  organism. 
If  we  look  rather  carefully  from 
all  sides  at  the  organ  called  the 
leaf,  we  find  that  the  materials  of 
which  it  is  composed  do  not  ap- 
pear to  be  everywhere  the  same. 
The  leaf  is  much  thinner  and  more 
delicate  in  some  parts  than  in 
others.  Holding  the  flat,  expanded 
blade  to  the  branch  is  a  little 
stalk,  the  petiole,  which  extends 
into  the  blade  of  the  leaf  as  a  se- 
ries of  little  veins  which  evidently 
form  a  framework  for  the  flat  blade 
somewhat  as  the  sticks  of  a  kite  hold  the  paper  in  place.  In  the 
same  manner  the  veins,  if  cut  crosswise  and  mounted  on  a  glass 
slide  under  the  compound  microscope,^  show  that  they  are  made 
up  of  building  material  which,  although  microscopic  in  size,  yet 
differs  considerably  from  other  material  in  the  same  part  of  the 
vein.  The  smallest  units  of  building  materia]  of  the  plant  or  ani- 
mal disclosed  by  the  compound  microscope  are  called  cells.  The 
organs  of  a  plant  or  animal  are  built  of  these  tiny  structures. 

Tissues.  —  The  cells  which  form  certain  parts  of  the  veins,  the 
flat  blade,  or  other  portions  of  the  plant,  are  often  found  in  groups 

*  For  a  study  of  the  compound  microscope,  see  Hunter  and  Valentine,  Manual,  page  3. 


Section  through  the  blade  of  a  leaf,  as 
seen  under  the  compound  micro- 
scope ;  /,  air  spaces,  which  com- 
municate with  the  outside  air. 


fafranr  ubrart 

M  r  State  Colkn* 


PROTOPLASM   AND  THE  CELL 


25 


or  collections,  the  cells  of  which  are  alike  in  size  and  shape  Such 
a  collection  of  cells  is  called  a  tissue.  Examples  of  tissues  are  the 
cells  covering  the  outside  of  the  human  body,  the  cells  which  col- 
lectively allow  of  movement,  the  so-called  muscles;  the  material 
that  forms  the  framework  to  which  the  muscles  are  attached,  the 
bony  tissues;   and  many  others.^ 

Cells.  —  A  cell  may  he  defined  as  the  smallest  bit  of  living  matter 
that  can  live  alone.  All  plant  and  animal  cells  appear  to  be  alike 
in  the  fact  that  every  living  cell  possesses  a  structure  known  as 
the  nucleus,  which  is  found  within  the  body  of  the  cell.  The 
nucleus    is    composed    of  q 

/<^i-fi:  v-H-^-'  :--"■  v:.•••■.".■/v-v<^-;-■^^i 


living  matter  like  the  rest 
of  the  cell,  although  it 
seems  to  differ  in  some 
chemical  way  from  that 
part  of  the  cell  surround- 
ing it.  This  is  seen  when 
a  plant  or  animal  is  placed 
in  a  liquid  containing 
some  dye  such  as  log- 
wood. Certain  bodies  in 
the  nucleus  take  up  the 
stain  much  more  readily 
than  the  rest  of  the  liv- 
ing matter  of  the  cell, 
taking  on  a  deep  black 
color.  They  are  thus 
called  the  chromosomes 
(color-bearing  bodies).^ 


Nn 


J.rt.-  '^?^^r^f 


>f!^'. 


r-K 


Diagram  of  a  cell  (after  Wilson).  The  cell  protoplasm 
contains  cell  food  (C./.) ;  spaces  contain  liquid  cell 
sap  {C.s.) ;  just  above  the  nucleus  (iV./.)  is  a  struc- 
ture called  the  centrosome  (c\  which  aids  in  cell 
division;  within  the  nucleus  are  chromosomes 
(N.n.),  which  form  a  network;  t.n.,  nucleolus. 


1  A  very  simple  tissue  that  may  be  studied  as  an  introductory  study  with  the 
microscope  is  a  thin  section  of  elder  or  pith,  mounted  in  water  or  glycernie  (dilute) 
on  a  glass  slide.  (See  Hunter  and  Valentine,  Manual,  page  7.)  The  study  of  yeast 
may  be  introduced  at  this  point  if  microscopes  are  available;  at  any  rate  demon- 
stration materifil  showing  isolated  cells  and  tissues  should  here  be  shown. 

2  The  chromosomes,  which  are  believed  to  be  always  definite  in  number  for  every 
tissue  cell,  are  of  much  interest  to  scientists.  It  is  found  that  each  time  a  cell 
splits  to  form  two  new  cells,  the  chromosomes  split  in  half  and  an  equal  number 
of  parts  go  into  the  nucleus  of  each  new  cell  thus  formed. _  These  chromosomes  are 
supposed  to  be  the  bearers  of  the  qualities  which  we  believe  can  be  handed  down 
from  plant  to  plant  and  from  animal  to  animal ;  in  other  words,  the  mheritable 
qualities  which  make  the  offspring  like  its  parents. 


26 


BOTANY 


Protoplasm.  —  The  living  matter  of  which  all  cells  are  formed 
is  known  as  'protoplasm  (from  two  Greek  words  meaning  first 
form). 

The  bulk  of  the  nucleus  is  filled  with  a  fluid;  in  some  nuclei  a 
body  known  as  a  nucleolus  is  found;  it  does  not  seem  to  be  a 
constant  structure.     The  protoplasm  surrounding  the  nucleus  is 

called  cytoplasm  be- 
cause it  makes  up  the 
body  of  the  cell.  The 
nucleus  plays  a  very 
important  part  in  the 
life  of  a  cell.  Cells 
grow  to  a  certain  size 
and  then  split  into  two 
new  cells.  In  this  pro- 
cess, which  is  of  very 
great  importance  in  the 
growth  of  both  plants 
and  animals,  the  nu- 
cleus divides  first.  The 
chromosomes  also  divide,  each  splitting  lengthwise  so  that  an 
equal  number  go  to  each  of  the  two  cells  formed  from  the  old 
cell.  Lastly,  the  cytoplasm  separates  and  two  new  cells  are 
formed.  This  process  is  known  as  fission.  It  is  the  usual 
method  of  growth  found  in  the  tissues  of  plants  and  animals. 

The  protoplasm  in  some  cells  collects  into  little  bodies  called  plastids. 
In  plant  cells  the  plastids  are  frequently  colored  green.  This  green  coloring 
matter,  which  is  found  only  in  plant  cells,  is  called  chlorophyll  and  green 
plastids  are  called  chlorophyll  bodies.  The  cytoplasm  of  a  cell  contains 
spaces,  which  are  usually  filled  with  a  fluid  known  as  cell  sap.  These  spaces 
in  the  cytoplasm  are  given  the  name  of  vacuoles.  Frequently  non-living 
materials  are  found  within  the  cytoplasm  of  the  cell. 

The  cell  is  surrounded  by  a  very  delicate  living  structure  called  the  cell 
membrane.  This  is  so  thin  that  it  is  impossible  to  get  a  microscope  of  power 
enough  to  throw  any  light  on  its  structure.  Outside  this  membrane  a  wall 
is  formed  by  the  activity  of  the  protoplasm  in  the  cells  of  plants.  In  the 
cells  of  the  pith  it  was  the  wall  of  cellulose  or  wood  that  you  saw  under  the 
microscope.  The  wood  used  in  building  is  made  up  of  the  dead  walls  of 
plant  cells. 


Stages  in  the  division  of  one  cell  to  form  two  cells.  Note 
the  separation  of  the  chromosomes  in  the  nucleus. 
Which  part  of  the  cell  divides  first  ? 


PROTOPLASM   AND   THE  CELL 


27 


Structure  of  Protoplasm.  —  Protoplasm,  when  viewed  under  a  high 
magnification  of  a  compound  microscope,  is  a  grayish,  almost  fluid  mass,  seem- 
ingly almost  devoid  of  any  structure.  A  careful  observer  will,  however,  find 
that  the  material  seems  to  be  made  of  a  ground  mass  of  fluid  with  innumer- 
able granules  of  various  size  and  form  floating  in  the  fluid  portion.  Other 
observers  believe  protoplasm  to  consist  of  a  fluid  groundwork  with  in- 
numerable tiny  threads  scattered  through  it,  each  thread  being  more  or  less 
firmly  united  with  other  threads  of  the  mass.  Still  other  scientists  hold  that 
protoplasm  has  essentially  the  structure  of  an  emulsion  or  froth  or  foam.  To 
them  the  fine  structure  resolves  itself  into  a  collection  of  very  minute  bub- 
bles. Doubtless  all  of  the  observers  are  right  in  part,  for  protoplasm  doubt- 
less assumes  all  of  the  above-mentioned  forms  in  different  plants  and  animals 
and  under  different  conditions.  But  we  must  also  bear  in  mind  that  when 
we  make  observations  on  protoplasm  it  may  be  already  dead  when  we 
examine  it  —  and  therefore  undoubtedly  greatly  changed  in  structure  —  or 
else  we  may  view  it  under  conditions  which  are  far  from  the  normal  con- 
ditions under  which  it  usually  exists  as  living  matter.  Finally,  the  instru- 
ment we  call  the  microscope,  although  seeming  to  be  nearly  perfect,  may 
not  always  give  to  our  eye  an  exact  representation  of  what  is  under  its  lenses. 


Cells  of  Various  Sizes  and  Shapes.  — 

Plant  cells  and  animal  cells  are  of  very 
diverse  shapes  and  sizes.  There  are 
cells  so  large  that  they  can  easily  be  seen 
with  the  unaided  eye;  for  example,  the 
root  hairs  of  plants  and  eggs  of  some 
animals.  On  the  other  hand,  cells  may 
be  so  minute  that  in  the  case  of  the 
plant  cells  we  call  bacteria,  several  mil- 
lion could  be  placed  on  a  dot  of  this 
letter  i.  The  forms  of  cells  may  be  ex- 
tremely varied  in  different  tissues;  they 
may  assume  the  form  of  cubes,  col- 
umns, spheres,  fiat  plates,  or  may  be  so 
irregular  that  description  is  impossible. 
One  kind  of  tissue  cell,  found  in  man, 
has  a  body  so  small  as  to  be  quite  in- 
visible to  the  naked  eye,  although  it 
has  a  prolongation  several  feet  in  length. 
Such  are  some  of  the  cells  of  the  ner- 


~iJ  n  hfijf 

nmWk 


Animal  cell,  showing  netlike 
structure  of  the  protoplasm. 
(After  Verworn.) 


28  BOTANY 

vous  system  of  man  and  other  large  animals,  as  the  ox,  elephant, 
and  whale. 

Varying  Sizes  of  Living  Things.  —  Plant  cells  and  animal  cells  may 
live  alone  or  they  may  form  collections  of  cells  as  tissues.  Some  plants  are  so 
simple  in  structure  as  to  be  formed  of  only  one  kind  of  tissue  cells.  Usually 
living  organisms  are  composed  of  several  groups  of  such  tissues.  Examples 
have  been  given.  It  is  only  necessary  to  call  attention  to  the  fact  that  such 
collections  of  tissues  may  form  organisms  so  tiny  as  to  be  barely  visible  to  the 
eye;  as,  for  instance,  some  water-loving  flowerless  plants  or  many  of  the  tiny 
animals  living  in  fresh  water  or  salt  water,  such  as  the  hydra,  small  worms, 
and  tiny  crustaceans.  On  the  other  hand,  among  animals  the  bulk  of 
the  elephant  and  whale,  and  among  plants  the  big  trees  of  California,  stand 
out  as  notable  examples. 

Relation  to  Organic  and  Inorganic  Matter.  —  The  inorganic 
matter  covering  the  earth,  as  air  and  water,  and  forming  the  great 
mass  of  its  bulk,  is  made  use  of  by  plants  and  animals.  The  latter 
make  their  homes  in  earth,  air,  or  water ;  they  breathe  the  oxygen 
of  the  atmosphere;  they  use  the  water  for  drinking;  but  in  the 
main  their  food  consists  of  organic  matter.  Plants,  on  the  other 
hand,  use  the  elements  contained  in  the  soil,  air,  and  water,  not 
only  for  food,  but  also  to  make  the  living  matter  of  their  own 
bodies.  In  some  mysterious  way,  of  which  we  shall  later  learn 
something,  plants  take  up  inorganic  and  organic  substances  from 
the  soil  and  air  and  transform  them  into  organic  matter.  This 
organic  matter  in  turn  becomes  food  for  animals. 

In  the  last  chapter  we  found  that  the  classes  of  substances  in 
an  animal  or  plant  and  the  organic  food  substances  have  a 
similar  composition.  Let  us  now  consider  chemically  the  sub- 
stance which  forms  the  basis  of  all  living  things. 

Protoplasm,  —  Living  matter,  when  analyzed  by  chemists  in  the 
laboratory,  seems  to  have  a  very  com.plex  chemical  composition. 
It  is  somewhat  like  a  proteid  in  that  it  always  contains  the  ele- 
ment nitrogen.  It  also  contains  the  elements  carbon,  hydrogen, 
oxygen,  and  a  little  sulphur,  and  perhaps  phosphorus.  Calcium, 
iron,  silica,  sodium,  potassium,  and  other  mineral  matters  are 
usually  found  in  very  minute  quantities  in  its  composition.  We 
believe  that  the  matter  out  of  which  plants  and  animals  are 
formed,  although  a  very  complex  building  material  and  almost 


PROTOPLASM   AND   THE  CELL  29 

impossible  of  correct  analysis,  is  nevertheless  composed  of  cer- 
tain chemical  elements  which  are  always  present.  To  this  living 
matter  the  name  protoplasm  has  been  given. 

Protoplasm,  then,  is  made  up  of  certain  chemical  elements, 
combined  in  definite  proportions.  What  is  of  far  more  impor- 
tance to  us  is  the  fact  that  it  is  distinguished  by  certain  properties 
which  it  possesses  and  which  inorganic  matter  does  not  possess. 

Properties  of  Protoplasm.  —  Plants  and  animals  are  largely  made 
up  of  living  matter.     Let  us  study  its  properties:  — 

(1)  It  responds  to  influences  or  stimulation  from  without  its 
own  substance.  Both  plants  and  animals  are  sensitive  to  touch 
or  stimulation  by  light,  heat,  or  electricity.  Leaves  turn  toward 
the  source  of  light.  Some  animals  are  attracted  to  light  and 
pthers  repelled  by  it;  the  earthworm  is  an  example  of  the  latter. 
Many  other  instances  might  be  given.  Protoplasm  is  thus  said 
to  be  irritable. 

(2)  Protoplasm  has  the  power  to  move  and  to  contract.  Muscular 
movement  is  a  familiar  instance  of  this  power.  Plants  move 
their  leaves  and  other  organs.    One-celled  animals  change  thefr  form. 

(3)  Protoplasm  has  the  power  of  taking  up  food  materials,  of  se- 
lecting the  materials  which  can  be  used  by  it,  and  of  rejecting  the  sub- 
stances that  it  cannot  use.  A  commercial  sponge,  the  dried  skeleton 
of  an  animal,  if  placed  in  water,  will  swell  up  with  the  water 
absorbed  by  it,  but  the  water  thus  taken  in  is  not  used  by  the 
dead  skeleton.  Protoplasm,  however,  in  the  tiny  parts  of  the 
root  of  a  plant  called  the  root  hairs,  takes  in  only  the  material 
w^hich  will  be  of  use  in  forming  food  or  new  protoplasm  for  the 
plant.  An  animal  selects  only  such  food  as  it  wants,  and  refuses 
to  eat  material  that  it  does  not  use  as  food. 

(4)  Protoplasm  grows,  not  as  inorganic  objects  grow,  from  the  out- 
side,^ but  by  a  process  of  taking  in  food  material  and  then  changing 
it  into  living  material.  To  do  this  it  is  evident  that  the  same 
chemical  elements  must  enter  into  the  composition  of  the  food 
substances  as  are  found  in  living  matter.     The  simplest  plants 

^  Experiment.  — •  Make  a  strong  solution  of  alum  (two  spoonfuls  of  powdered  alum 
to  half  a  glass  of  water).  Suspend  in  the  glass  a  thread  with  a  pebble  attached  to 
the  lower  end.     Notice  where  and  how  crystals  of  alum  grow. 


so  BOTANY 

and  animals  have  this  wonderful  power  as  well  developed  as  the 
most  complex  forms  of  life. 

(5)  Protoplasm,  he  it  in  the  body  of  a  plant  or  an  animal,  uses 
oxygen.  It  breathes.  Thus  the  food  substances  taken  into  the 
body  are  oxidized,  and  either  release  energy  for  growth,  move- 
ment, etc.,  or  form  new  protoplasm. 

(6)  Protoplasm  has  the  power  to  rid  itself  of  waste  materials, 
especially  those  which  might  be  harmful  to  it.  A  tree  sheds  its 
leaves  partly  to  get  rid  of  the  accumulation  of  mineral  matter  in 
the  leaves.  Plants  and  animals  alike  pass  off  the  carbon  dioxide 
which  results  from  the  very  processes  of  living,  the  oxidation  of 
foods  or  parts  of  their  own  bodies.  Animals  eliminate  wastes 
containing  nitrogen  through  the  skin  and  the  kidneys. 

(7)  Protoplasm  can  reproduce,  that  is,  form  other  matter  like  itself. 
New  plants  are  constantly  appearing  to  take  the  places  of  those 
that  die.  The  supply  of  living  things  upon  the  earth  is  not  de- 
creasing; reproduction  is  constantly  taking  place.  In  a  general 
way  it  is  possible  to  say  that  plants  and  animals  reproduce  in  a 
very  similar  manner.     We  shall  study  this  more  in  detail  later. 

To  sum  up,  then,  we  find  that  living  protoplasm  has  the  prop- 
erties of  sensibility,  motion,  growth,  and  reproduction  alike  in  its 
simplest  state  as  a  one-celled  plant  or  animal  and  when  it  enters 
into  the  composition  of  a  highly  complex  organism  such  as  a  tree, 
a  dog,  or  a  man. 

Books  for  Referencb 

for  the  pupil. 

Leavitt.    OvUines  of  Botany.    American  Book  Company. 

Atkinson.    First  Stvdies  of  Plant  Life.    Chap.  XI.    Ginn  and  Company. 

FOR  THE   TEACHER 

Goodale.    Physiological  Botany.    American  Book  Company. 

Green.     Vegetable  Physiology.     J.  and  A.  Churchill. 

Huxley  and  Martin.     Course  of  Elementary  Instruction  in  Practical  Biology.    The 

Macmillan  Company. 
Sedgwick  and  Wilson.     General  Biology.     Henry  Holt  and  Company. 
Wilson.     The  Cell  in  Development  and  Inheritance.    The  Macmillan  Company. 


IV.    FLOWER 


A  flower  of  Sedum,  from  the  side; 
^,  anther  of  stamen;  C,  carpel; 
F,  filament;  P,  petal;  S,  sepal. 


Structure  of  a  Simple  Flower.  —  For  the  following  exercise,  the 
buttercup  and  Sedum  (stonecrop)  are  good.  They  may  be  ob- 
tained in  the  fall.^ 

The  expanded  portion  of  the  flower  stalk, 

which  holds  the  parts  of  the  flower,  is  called 

the  receptacle.     The  green  leaflike  parts  cover- 
ing the  unopened  flower  are  called  the  sepals. 

Sometimes  the  sepals  are  all  joined  or  united 

in  one  piece.    Taken  together,  they  are  caUed 

the  calyx.     Notice  that  the  sepals  come  out 

in  a  circle  or  whorl  on  the  flower  stalk.    How 

many  sepals  do  you  find  ?     In  what  respect 

do  they  resemble  leaves?      Are  there  any 

evidences  as  to  their  use  or  function  ? 

The  more  brightly  colored  structures  are  the 

petals.     Taken  together,  they  form  the  co- 
rolla.    The  corolla  is  of  importance,  as  we 

shall  see  later,  to  make  the  flower  conspicuous. 
Compare  the   petals  and  sepals  In   this 

flower.    Are  sepals  and  petals  in  any  respects 

like  leaves  ? 

A   flower,   however,    could   live   without 

sepals  or  petals  and  still  do  the  work  for 

which  it  exists.     The  essential  organs  of  the  flower  are  within  the  so-called 

floral  envelope.  They  consist  of  the  stamens 
and  carpels  (or  pistils).  The  latter  are  in  the 
center  of  the  flower.  The  structures  with 
the  knobbed  ends  are  called  stamens.  How 
many  stamens  do  you  find,  and  what  is 
their  position  ? 

In  a  single  stamen  the  boxlike  part  at  the 
end  is  the  anther;  the  stalk  is  called  the  fila- 
ment. The  anther  is  in  reality  a  hollow  box 
in  which  a  dustlike  material  called  pollen  is 
produced.  It  is  necessary  for  the  life  of  the 
plant  that  the  pollen  get  out  of  the  anther. 
Try  to  find  how  it  gets  out. 

Pistil.  —  Each  carpel  or  pistil  is  composed 
of  a  rather  stout  base  called  the  ovary,  and  a 
more  or  less  lengthened  portion  rising  from 
the  ovary  called  the  style.  The  upper  end 
of  the  style,  which  in  some  cases  is  somewhat 
broadened,  is  called  the  stigma.       The  stig- 

matic  surface  usually  secretes  a  sweet  fluid  in  which  grains  of  pollen  from 

flowers  of  the  same  kind  can  grow. 

*  See  Hunter  and  Valentine,  Manual,  page  54. 

31 


A  flower  of  Sedum  from  above; 
A,  anther;  C,  carpel;  F,  fila- 
ment; P,  petal;  S,  sepal. 


32 


BOTANY 


n' 


Draw  one  of  the  flowers  in  your  notebook.  Show  the  flower  stalk  or 
'peduncle  and  all  the  above-mentioned  parts  carefully  labeled.  Keep  any 
notes  that  you  may  have  made  on  the  work  on  the  flower.^ 

Pollen.  —  Pollen  grains  of  various  flowers,  when  seen  under  the 
microscope,   differ  greatly   in   form   and   appearance.     Some  are 

relatively  large,  some  small,  some 
rough,  others  smooth,  some  spheri- 
cal, and  others  angular.  They  all 
agree,  however,  in  having  a  thick 
wall,  with  a  thin  membrane  under 
it,  the  whole  inclosing  a  mass  of 
protoplasm.  At  an  early  stage  the 
pollen  grain  contains  but  a  single 
cell.  When  we  see  it,  however,  we 
can  distinguish  two  nuclei  in  the 
protoplasm.  Hence  we  know  that 
at  least  two  cells  exist  there. 


n 


A  pollen  grain  highly  magnified.  It 
contains  two  nuclei  {n,  n')  at  the 
stage  here  represented. 


Experiment.  —  Germination  of  the  Pollen  Grain.  Make  a  solution  of 
fifteen  grams  of  granulated  sugar  in  one  hundred  cubic  centimeters  of 
water.  Place  on  each  of  several  glass  microscopic  slides  a  few  drops  of  the 
solution  and  sprinkle  with  pollen  taken  from  well-opened  flowers  of  sweet 
pea  or  a  nasturtium.  Place  on  the  slides  some  very  thin  and  small  bits  of 
cover  glass,  and  with  these  prop  up  the  cover  slip  which  is  placed  over  the 
sugar  solution.  Leave  them  for  a  few  hours  under  a  bell  jar  with  a  piece 
of  moist  sponge  to  keep  the  air 
in  the  jar  moist.  Examine  the 
slides  from  time  to  time  under 
the  microscope.  The  grains  of 
pollen  will  be  found  to  germinate, 
a  long  threadlike  mass  of  proto- 
plasm growing  from  it  into  the 
sugar  solution.  The  presence  of 
this  sugar  solution  was  sufficient 
to  induce  growth. 

Demonstration  under  Micro- 
scope.—  Pollen  tubes  growing  in 
dilute  sirup.  When  the  pollen 
grain  germinates,  one  of  the  nuclei  enters  the  threadlike  growth  (this  growth 
is  called  the  pollen  tube;  see  figure).  The  pollen  tube  is  therefore  a  long 
threadlike  cell,  which  is  artificially  stimulated  to  growth  bj^  the  sugar  solu- 
tion, but  which  in  nature  is  brought  into  existence  by  the  presence  of  the 
sweet  liquid  which  exudes  from  the  surface  of  the  stigma.  The  cell  which 
grows  into  the  pollen  tube  is  known  as  the  sperm  cell. 

Structure  of  the  Pistil.  —  Let  us  now  examine  the  structure  of  the  pistil 
more  in  detail.     (Use  for  this  purpose  any  large  lily.)  Cut  the  pistil  length- 

*  Laboratory  directions  for  other  work  on  flowers  may  be  found  in  Hunter  and 
Valentine.  Manual,  paeres  51-63. 


Three  stages  in  the  germination  of  the  pollen 
grain  in  sugar  solution.  Drawn  imder  the 
compound  microscope. 


FLOWERS 


33 


wise;  notice  that  the  style  appears  to  be  composed  of  rather  spongy 
material  m  the  interior;  the  ovary  is  hollow  and  is  seen  to  contain  a  num- 
ber of  rounded  structures 
which  appear  to  grow  out 
from  the  wall  of  the  ovary. 
These  are  the  ovules.  The 
compartments  in  which  they 
grow  are  called  the  locules. 
How  many  locules  do  you 
find  in  a  cross  section  of 
the  lily  ?  ^  That  part  of  the 
ovary  wall  from  which  the 
ovules  are  outgrowths  is 
called  the  placenta  (plu. 
placentcB).  How  many  pla- 
centae do  you  find,  and  how 
would  you  locate  them  with 
reference  to  the  outside  of 
the  ovary  ? 

Fertilization  of  the 
Flower.  —  The  ovules, 
under  certain  conditions, 
become  seeds.  An  expla- 
nation of  these  condi- 
tions may  be  had  if  we 
examine,  under  the  mi- 
croscope, a  very  thin 
section  of  a  pistil,  on 
which  pollen  has  begun 
to  germinate.  The  cen- 
tral part  of  the  style  is 
found  to  be  either  hollow 
or  composed  of  a  soft 
tissue  through  which  the 
pollen  tube  can  easily 
grow.  Upon  germina- 
tion, the  pollen  tube 
grows  downward  through 
the  spongy  center  of  the 
style,  follows  the  path  of  least  resistance  to  the  locule  of  the 
ovary,  and  there  grows  into  the  ovule.     It  is  believed  that  some 

^  The  structural  differences  in  the  flower  of  a  monocotyledon  and  dicotyledon 
may  well  be  pointed  out  here. 

hunter's  BIOL.  —  3 


Fertilization  of  the  ovule.  The  pollen  tubes  pass 
through  the  stigma  and  style,  finally  entering  the 
cavity  (locules)  of  the  ovary. 


34  BOTANY 

chemical  influence  thus  attracts  the  pollen  tube.  In  flowers  in 
which  the  style  is  short,  the  tube  reaches  the  ovule  in  the 
course  of  a  few  hours.  In  plants  with  a  long  style,  from  one 
to  several  days  may  elapse  before  the  pollen  tube  reaches  the 
locule  of  the  ovary.  Once  it  reaches  the  ovary,  the  tube  pene- 
trates an  ovule  by  making  its  way  through  a  little  hole  known  as 
the  micropyle.  It  then  grows  toward  a  clear  area  of  protoplasm 
known  as  the  embryo  sac.  The  embryo  sac  is  an  ovoid  area, 
microscopic  in  size,  filled  with  semifluid  protoplasm  containing 
several  nuclei.  (See  figure.)  One  of  the  nuclei,  with  the  proto- 
plasm immediately  surrounding  it,  is  called  the  egg  cell.  It  is  this 
cell  that  the  sperm  cell  of  the  pollen  tube  grows  toward ;  ultimately 
the  sperm  cell  reaches  the  egg  cell  and  unites  with  it.  The  two 
cells,  after  coming  together,  unite  to  form  a  single  cell.  This 
process  is  known  as  fertilization.  This  single  cell  formed  by  the 
union  of  the  pollen  tube  cell  or  sperm  and  the  egg  cell  is  now  called 
a  fertilized  egg. 

Development  of  Ovule  into  Seed.  —  The  primary  reason  for  the 
existence  of  a  flower  is  that  it  may  produce  seeds  from  which 
future  plants  will  grow.  The  first  beginning  of  the  growth  of  the 
seed  takes  place  at  the  moment  of  fertilization.  From  that  time 
on  there  is  a  growth,  within  the  ovule,  of  a  little  structure  called 
the  embryo.  The  embryo  will  give  rise  to  the  future  plant.  After 
fertilization  the  ovule  is  called  a  seed. 

History  of  the  Discoveries  regarding  Fertilization.  —  Although 
the  ancient  Greek  and  Roman  naturalists  had  some  vague  ideas 
on  the  subject  of  fertilization,  it  was  not  until  the  latter  part  of 
the  eighteenth  century  that  it  was  demonstrated  that  pollen  was 
necessary  for  the  growth  of  the  embryo  within  a  seed.  In  the 
latter  part  of  the  eighteenth  century  a  book  appeared  in  which  a 
German  named  Conrad  Sprengel  worked  out  the  facts  that  the 
structure  of  certain  flowers  seemed  to  be  adapted  to  the  visits  of 
insects.  Certain  facilities  were  offered  to  an  insect  in  the  way  of 
easy  foothold,  sweet  odor,  and  especially  food  in  the  shape 
of  pollen  and  nectar,  the  latter  a  sweet-tasting  substance  manu- 
factured by  certain  parts  of  the  flower  known  as  the  nectar  glands. 
Sprengel  further  discovered  the  fact  that  pollen  could  be  and  was 


FLOWERS 


35 


carried  by  the  insect  visitors  from  the  anthers  of  the  flower  to  its 
stigma. 

Pollination.  —  It  was  not  until  the  middle  of  the  nineteenth  cen- 
tury, however,  that  an  Englishman,  Charles  Darwin,  discovered 
the  true  relation  of  insects  to  flowers  by  his  investigations  upon 
the  cross-pollination  of  flowers.  By  pollination  we  mean  the 
transfer  of  pollen  from  an  anther  to  the  stigma  of  a  flower.  Self- 
pollination  is  the  transfer  of  pollen  in  one  flower ;  cross-pollination 
is  the  transfer  of  pollen  from  the  anthers  of  one  flower  to  the  stigma 
of  another  flower  of  the  same  kind.  It  was  found  by  Charles  Darwin 
—  and  it  has  since 
been  proved  many 
times — that  flow- 
ers which  were 
self-pollinated  did 
not  produce  so 
many  seeds,  or 
seeds  with  so 
much  vitality,  as 
those  which  were 
cross  -  pollinated. 
Microscopic  ex- 
amination of  the 
stigma  at  the  time 
of  pollination  also 
shows  that  the  pollen  from  another  flower  germinates  before 
the  pollen  which  has  fallen  from  the  anthers  of  the  same  flower. 
This  latter  fact  alone  in  most  cases  renders  it  impossible  for  a 
flower  to  produce  seeds  by  its  own  pollen.  Darwin  worked  for 
many  years  on  the  pollination  of  many  insect-visited  flowers,  and 
discovered  in  almost  every  case  that  showy,  sweet-scented, 
or  otherwise  attractive  flowers  were  adapted  or  fitted  to  be  cross- 
pollinated  by  insects.  He  also  found,  in  the  case  of  flowers  that 
were  inconspicuous  in  appearance,  often  a  compensation  appeared 
in  the  odor  which  rendered  them  attractive  to  certain  insects. 
The  so-called  carrion  flowers,  polUnated  by  flies,  are  examples, 
the  odor  in  this  case  being  like  decayed  flesh.     Other  flowers  open 


An  orchid,  a  flower  of  the   type  from  which  Charles  Darwin 
worked  out  his  theory  of  cross-poUination  by  insects. 


36  BOTANY 

at  night,  are  white,  and  provided  with  a  powerful  scent  so  as  to 
attract  night-flying  moths  and  other  insects.  We  shall  later  take 
up  some  of  the  many  cases  of  the  adaptation  of  the  parts  of  a 
flower  to  these  insect  callers.^  Flowers  adapted  to  be  cross- 
pollinated  by  insects  are  almost  invariably  irregular  in  shape. 
Let  us  now  consider  rather  in  detail  the  structure  of  the  sweet  pea, 
an  example  of  such  a  flower. 

Sweet  Pea.  —  The  sepals  are  of  almost  the  same  size  and  shape;  that  is, 
regular.  The  petals,  however,  are  quite  different  from  each  other  in  form.  If 
you  pull  off  the  parts  of  the  corolla  you  will  find  that  they  separate  naturally 
into  a  large  expanded  petal  at  the  top  of  the  flower;  this  is  called  the  vane  or 
standard;  two  petals  at  the  sides  called  the  wings,  and  a  curved  part  below 
called  the  keel,  the  latter  being  made  of  two  petals  joined  along  the  edge. 

A  corolla  of  this  kind  is  said  to  be  'papilionaceous  from  its  fancied  resem- 
blance to  a  butterfly.  What  other  plants  do  you  know  that  have  flowers  of 
this  shape? 

If  you  press  the  point  of  a  pencil  down  upon  the  keel  of  the  flower,  holding 
it  in  a  natural  position,  you  will  soon  find  that  the  point  has  taken  up  some 
pollen.     Evidentl}''  a  bee  might  carry  off  pollen  in  the  same  manner. 

Now  remove  the  corolla  from  one  side  of  the  flower  so  as  to  show  the 
stamens  and  pistil.  Notice  that  the  stamens  are  separated  into  two  groups, 
those  in  one  group  united  by  their  filaments  to  each  other.  How  many  are 
there  in  each  group  ?  This  condition  of  stamens  is  said  to  be  diadelphous. 
Draw  the  flower  from  the  side,  showing  the  above  parts  before  j^ou  pull  off 
the  stamens.  Look  for  the  three  parts  of  the  pistil.  Draw  and  label  them. 
Notice  the  little  hairs  covering  parts  of  the  pistil;  can  you  imagine  their  use  ? 
In  old  flowers  you  can  see  that  the  ovary  is  forming  the  characteristic  pod 
of  the  pea  family. 

Insects  as  Pollinating  Agents.  —  We  have  seen  in  a  general  way 
that  insects  assist  in  the  cross-pollination  of  flowers.  Let  us  now 
turn  our  attention  to  the  insects  to  see  how  in  their  structure  and 
habits  they  are  adapted  to  play  the  important  part  that  they  fill 
in  the  cross-pollination  of  flowers.  No  one  who  sees  a  hive  of 
bees  with  their  wonderful  communal  life  can  fail  to  see  that  these 
insects  play  a  great  part  in  the  life  of  the  flowers  near  the  hive. 
A  famous  observer  named  Sir  John  Lubbock  tested  bees  and 
wasps  to  see  how  many  trips. they  made  daily  from  the  hive  to 
the  flowers,  and  found  that  the  wasp  went  out  on  116  visits 
during  a  working  day  of  16  hours,  while  the  bee  made  but  a  few 

^  At  this  point,  at  least  one  field  trip  should  be  introduced  for  the  purpose  of 
studying  under  natural  conditions  tlie  cross-pollination  of  flowers  by  insects.  For 
suggestions  for  such  a  trip,  see  Hunter  and  Valentine,  Manual,  page  207.  Many 
of  the  following  exercises  on  fall  flowers  may  profitably  be  taken  in  the  field  arid 
reported  on  by  the  pupil  as  class  exercises.  Excellent  suggestions  for  a  field  trip 
may  be  found  in  Andrews,  Botany  All  the  Year  Round. 


FLOWERS 


37 


less  visits,  and  worked  only  a  little  less  time  than  the  wasp  worked. 
It  is  evident  that  in  the  course  of  so  many  trips  to  the  fields  a 
bee  must  light  on  and  cross-pollinate  many  hundreds  of  flowers. 


Bumblebees ;  a,  queen  ;  6,  worker  ;  c,  drone. 

Laboratory  Study  of  a  Bumblebee.  —  The  careful  study  of  the  bumblebee 
will  give  us  some  insight  into  the  manner  in  which  the  bee  transfers  pollen. 
Living  specimens  may  be  chloroformed  and  then  used  dry^  or  material  which 
has  been  preserved  in  formol  or  alcohol  will  answer  the  purpose.  The  body 
of  an  insect  is  divided  into  three  regions;  these  may  easily  be  found  in  the 
bee.  The  anterior  or  front  part  is  the  head,  the  middle  is  the  thorax,  and 
the  posterior  or  hind  part  is  the  abdomen.  The  abdomen  in  the  working 
bees  is  terminated  in  a  sharp  sting.  Look  carefully  at  the  abdomen;  you 
will  find  it  is  cut  up  into  a  series  of  little  rings  which  taper  off  at  the  hind 
end  of  the  body.  These  rings  are  called  segments.  Notice  that  the  legs 
and  wings  are  attached  to  the  thorax.  The  wings  are  found  on  the  dorsal 
or  upper  side  of  the  body,  the  legs  on  the  lower  or  ventral  surface.  Look 
at  a  leg  with  your  hand  lens.  Is  it  all  of  one  piece  or  jointed?  When  a 
plant  or  animal  structure  is  fitted  to  do  certain  kind  or  kinds  of  work,  we  say 
that  the  structure  is  adapted  to  its  functions.  Can  you  determine  how  the 
leg  is  adapted  for  movement  and  for  clinging  to  an  object?  Can  you  find 
any  parts  adapted  to  hold  pollen  ?  Notice  the  collection  of  stiff  hairs  on 
the  joint  next  the  body.  In  the  honeybee  these  hairs  are  so  arranged  that 
they  act  as  receptacles  for  pollen,  which  the  bee  stores  there  to  carry  home 
to  the  hive.    Bees,  wasps,  and  many  other  insects  use  pollen  as  food. 

The  body  of  the  bee,  as  well  as  the  head  and  legs,  are  more  or  less  com- 
pletely covered  with  tiny  hairs.  Are  the  hairs  any  better  developed  m 
certain  parts  of  the  body?  If  so,  do  you  think  they  would  be  of  use  in 
carrying  pollen,  and  why  ? 

Pollination  not  intended  by  the  Bee.  —  The  cross-pollination  of 
flowers  is  not  planned  by  the  bee;  it  is  simply  an  incident  in 
the  course  of  the  food  gathering.  The  bee  visits  a  large  number 
of  flowers  of  the  same  species  during  the  course  of  a  single  visit 
from  the  hive,  and  it  is  then  that  cross-pollination  takes  place. 

Field  Work.  —  In  any  locality  where  flowers  are  abundant,  try  to  answer 
the  following  questions:  How  many  bees  visit  the  locality  in  ten  minutes? 


38 


BOTANY 


How  many  other  insects  alight  on  the  flowers  ?  Do  bees  visit  flowers  of  the 
same  kinds  in  succession,  or  fly  from  one  flower  on  a  given  plant  to  another 
on  a  plant  of  a  different  kind  ?  If  the  bee  lights  on  a  flower  cluster,  does  it 
visit  more  than  one  flower  in  the  same  cluster? 

Is  Color  or  Odor  in  a  Flower  an  Attraction  to  an  Insect?  —  Try  to  decide 
whether  color  or  odor  has  the  most  effect  in  attracting  bees  to  flowers.  Sir 
John  Lubbock  tried  an  experiment  which  it  would  pay  a  number  of  careful 
pupils  to  repeat.  He  placed  a  few  drops  of  honey  on  glass  slips  and  placed 
them  over  papers  of  various  colors.  In  this  way  he  found  that  the  honey- 
bee, for  example,  could  evidently  distinguish  different  colors.  Bees  seemed 
to  prefer  blue  to  any  other  color.  Flowers  of  a  yellow  or  flesh  color  are 
preferred  by  flies.  It  would  be  of  considerable  interest  for  some  student  to 
work  out  this  problem  with  our  native  bees  and  with  other  insects.  Test 
the  keenness  of  sight  in  insects  by  placing  a  white  object  (a  white  golf  ball 
will  do)  in  the  grass  and  see  how  many  insects  will  alight  on  it.  Try  to 
work  out  some  method  by  which  you  can  decide  whether  a  given  insect  is 
attracted  to  a  flower  by  odor  alone. 

The  Eyes  of  the  Bumblebee.  —  Look  carefully  at  th&  large  eyes  located  on 
the  sides  of  the  head.  They  are  made  up  of  a  large  number  of  little  units, 
each  of  which  is  considered  to  be  a  very  simple  e3^e.  The  large  eyes  are 
therefore  called  the  compound  eyes.  All  insects  are  provided  with  com- 
pound eyes,  and  in  addition  to  these  (in  some  cases)  with  simple  eyes.  The 
simple  eyes  of  the  bee  may  be  found  by  a  careful  observer  in  front  and  above 
the  compound  eyes. 


One  would  suppose  that  with  so  many  eyes  the  sight  of  insects 
would  be  extremely  keen,  but  such  does  not  seem  to  be  the  case. 

Insects  can,  as  we  have  already 
learned,  distinguish  differences  in 
color  at  some  distance,  but  they 
do  not  seem  to  be  able  to  make 
out  form  at  any  distance.  To 
make  up  for  this,  they  appear  to 
have  an  extremely  well-developed 
sense  of  smell.  Insects  can  dis- 
tinguish at  a  great  distance  odors 
which  to  the  human  nose  are  in- 
distinguishable. Night-flying  in- 
sects, especially,  find  the  flowers 
by  the  odor  rather  than  by  color. 
The  organ  which  perceives  odors 
is  located  on  the  feelers  on  the 
head. 

Nectar  and  Nectar  Glands.  —  The  bee  is  attracted  to  a  flower 
for  food.     This  food  may  consist  of  pollen  and  nectar.     Nectar  is  a 


A   lily;    P,   petal;     »S.,    stamen    (anther); 
SEP.,  sepal;    St.,  pistil  (stigma). 


FLOWERS 


39 


Head  of  the  bumblebee; 
a,  antenna;  g,  tongue 
used  in  licking  the 
nectar  from  flowers; 
m,  maxillae. 


sugary  solution  that  is  formed  in  the  flower  by  little  collections  of 
cells  called  the  nectar  glands.  The  nectar  glands  are  usually  so 
placed  that  to  get  to  them  the  insect  must 
first  brush  the  stamens  and  pistil  of  the 
flower.  Frequently  the  location  of  the  necta- 
ries (nectar  glands)  is  made  conspicuous  by 
brightly  colored  markings  on  the  corolla  of 
the  flower.  The  row  of  dots  seen  in  the  tiger 
lily  is  an  example.  You  may  easily  find  other 
instances  of  nectar  guides,  as  they  are  called. 
Look  for  them  in  any  of  the  common  fall 
flowers. 

Mouth  Parts  of  the  Bee.  —  The  mouth  of  the  bee  is 
adapted  to  take  in  the  foods  we  have  mentioned, 
and  is  used  for  many  other  purposes  for  which  a 
more  highly  developed  animal,  man,  would  use  the 
hands  and  fingers.  The  honeybee  laps  or  sucks  nec- 
tar from  flowers,  it  chews  the  pollen,  and  it  uses 
part  of  the  mouth  as  a  trowel  in  making  the  honey- 
comb. A  glance  at  the  figure  shows  us  that  the 
mouth  parts  of  the  bee  are  complex.  The  parts  con- 
sist of  a  pair  of  very  small  jaws  or  mandibles,  certain  other  structures, 
maxillae,  part  of  the  lower  lip  called  the  labial  palps,  and  a  long  tonguelike 
structure  called  the  ligula.  Watch  a  bee  on  a  flower.  Try  to  make  out 
what  parts  of  the  mouth  are  used  in  taking  nectar  and  in  gathering  pollen. 
Make  a  drawing  of  the  bumblebee,  twice  natural  size,  showing  as  many 
of  the  structures  we  have  just  described  as  possible.  Label  the  parts  care- 
fully and  put  it  in  your  note- 
book. It  will  be  interesting 
to  compare  this  drawing  with 
the  drawings  you  make  later 
in  the  year  when  you  study 
other  insects.  You  will  be 
surprised  to  find  how  much 
you  improve  in  drawing. 

Other  Insect  Visitors.  — ■ 
Other  insects  besides  the 
bee  are  pollen  carriers  for 
flowers.  Among  the  most 
useful  are  moths  and  but- 
terflies. Both  of  these 
insects  feed  only  on  nectar,  which  they  suck  through  a  long  tube- 
like proboscis.     The  heads  and  bodies  of  these  insects  are  more 


Swallowtail  butterfly  pollinating  clover.    Cross  polli- 
nation of  clover  is  usually  effected  by  bumblebees. 

Photograph  by  Davison. 


40 


BOTANY 


or  less  thickly  covered  with  hairs,  and  the  wings  are  thatched  with 
hairlike,  tiny  scales.  All  these  structures  are  of  use  to  the 
flower  because  they  collect  and  carry  pollen.  On  each  side  of  the 
head  of  a  butterfly  is  a  long,  fluffy  structure,  the  palp.  This 
collects  and  carries  a  large  amount  of  pollen,  which  is  deposited 
upon  the  stigmas  of  other  flowers  when  the  butterfly  pushes  its 
head  down  into  the  flower  tube  after  nectar. 

Flies  and  some  other  insects  are  agents  in  cross-pollination,  as 
we  shall  see  during  some  of  our  later  studies.     Humming  birds 

are  also  active  agents 
in  some  flowers.  Snails 
are  said  in  rare  in- 
stances to  carr}^  pollen. 
Man  and  the  domesti- 
cated animals  un- 
doubtedly frequently 
pollinate  flowers  by 
brushing  past  them 
through  the  fields. 

Field  Flowers.  —  Let  us 
now  take  up  some  com- 
mon  wild   flowers   easily 
found  in  the  fall  of  the 
year,  and  work  out  the  re- 
lation of  the  parts  of  the 
flower  to  its  insect  visit- 
ors.    Remember  that  the 
important  part  of  these 
exercises  is  to  find  how 
and  by  what  means  the 
flower  is  adapted  or  fitted  to  receive  the  visits  of  insects.     This  work  can 
be  done  best  on  field  trips,  but  it  can  readily  be  modified  so  as  to  be  useful 
as  a  schoolroom  exercise. 

The  Evening  Primrose  (Onagra  biennis) .  —  The  habitat  preferred  by 
this  flower  is  dry  fields,  roadsides,  or  waste  places.  The  yellow  flowers  are 
found  in  long,  upright,  densely  crowded  clusters.  A  flower  cluster  in  which 
the  individual  flowers  have  no  flower  stalks  or  pedicles,  with  one  main  axis 
to  the  cluster,,  is  called  a  spike.  Notice  that  young  and  old  flowers  and 
fruits  are  all  on  the  same  cluster.  Where  are  the  youngest  flowers  located 
in  the  cluster?  Is  there  any  flower  at  the  end  of  the  main  stalk?  Could 
you  determine  in  advance  the  length  of  the  flower  cluster  ?  Such  a  cluster 
is  said  to  be  indeterminate.  Why?  Study  a  single  open  flower.  Note 
the  caljrx  and  corolla;  are  the  parts  distinct?  How  many  petals  do  you 
find  ?  Notice  that  there  are  eight  stamens  and  that  the  stigma  is  four-parted. 
Cut  the  ovary  in  cross  section  and  see  how  many  locules  there  are. 


A  humming  bird  just  about  to  cross-pollinate  a  flower. 


FLOWERS  41 

When  a  flower  has  each  circle  of  parts,  as  the  sepals,  petals,  stamens,  and 
pistils  made  up  of  a  certain  number  of  divisions,  or  wnon  they  appear  in  multi- 
ples of  that  number,  the  flower  is  said  to  be  symmetricat.  Here  we  see  a 
very  striking  example  of  symmetry  in  a  flower. 

The  chief  attraction  to  insects  is  the  nectar  which  is  formed  in  nectar 
glands  at  the  base  inside  the  slender  tubular  corolla.  Information  is  given 
to  the  insects  of  the  contents  by  a  faint,  sweet  odor.  This  flower  is  not 
visited  by  many  day-flying  insects.  Can  you  determine  the  names  of  any 
that  do  come  by  day?  At  night  the  flower  opens  more  widely  and  the 
scent  becomes  much  more  noticeable.  Moths  are  its  chief  night  visitors. 
The  long  proboscis  is  thrust  into  the  flower  and  quickly  withdrawn,  but 
usually  a  little  pollen  is  carried  off  on  the  palps,  to  be  left  on  the  next  flower 
visited. 

Try  to  determine  what  other  insects,  if  any,  visit  the  evening  primrose  at 
night. 

Draw  a  single  flower  spHt  open  lengthwise  to  show  the  position  of  the 
parts,  and  especially  any  adaptations  to  insect  pollination.  Look  for  any 
special  means  for  the  prevention  of  self-pollination.      Label  all  the  parts. 

Butter  and  Eggs  (Linaria  linaria).  —  From  July  to  October  this  very 
abundant  weed  may  be  found  especially  along  roadsides  and  in  sunny  fields. 
The  flower  cluster  forms  a  tall  and  conspicuous  spike.  Can  you  see  any 
advantages  to  a  plant  in  bearing  its  flowers  in  clusters? 

Describe  the  general  shape  of  the  flowers.  The  corolla  projects  into  a 
spur  on  the  lower  side ;  an  upper  two-parted  lip  shuts  down  upon  a  lower 
three-parted  lip.  The  four  stamens  are  in  pairs.  What  is  peculiar  in  their 
position  and  structure?  Notice  the  position  of  the  pistil.  Could  self- 
pollination  easily  occur?  (The  stamens  of  two  lengths  may  allow  self- 
pollination  in  stormy  weather,  when  insects  fail  to  reach  the  flower.) 

Notice  that  certain  parts  of  the  corolla  are  more  brightly  colored  than 
the  rest  of  the  flower.  This  color  is  a  guide  to  insects.  How  might  it  help 
them  in  this  flower  ? 

Push  a  pencil  between  the  two  lips  of  the  flower.  Does  the  pencil  touch 
the  stamens  ?  If  a  bee  pushes  aside  the  lips,  would  it  be  likely  to  take  any 
pollen  from  the  stamens  ?  Do  you  think  other  insects  than  bees  would  be 
likely  to  aid  the  flower  in  pollination  ? 

Draw  the  flower  from  the  side,  cut  lengthwise  to  show  the  position  of 
stamens  and  pistil.     Make  this  drawing  diagrammatic. 

Moth  Mullein  {Verbascum  hlattaria).  —  The  moth  mullein  is  one  of  the 
most  beautiful  weeds,  despite  the  fact  that  few  blossoms  are  found  at 
any  given  time.  The  plant  flourishes  on  dry  waste  land,  roadsides,  and  open 
fields.  It  was  introduced  into  this  country  and  has  since  become  common 
here  and  in  Canada. 

The  flowers  are  found  in  a  long,  loose  raceme.  A  raceme  is  like  a  spike, 
except  that  each  flower  has  its  own  flower  stalk  developed.  Has  this 
cluster  yellow  or  white  flowers  ?  Into  how  many  parts  is  the  calyx  divided  ? 
The  corolla?  Is  the  corolla  perfectly  regular?  Notice  the  five  stamens; 
is  there  anything  peculiar  about  the  filaments?  Are  they  all  of  the  same 
length  ?  In  spite  of  the  fact  that  the  flower  is  called  moth  mullein,  it  is  not  pol- 
linated to  any  extent  by  moths.  Bees  and  flies  are  the  chief  pollen  bearers. 
Bees  which  alight  on  this  flower  do  so  for  the  purpose  of  collecting  pollen. 
This  they  usuaUy  gather  from  the  short  stamens  while  they  cling  to  the 
longer  ones.  As  the  bee  lights  on  another  flower,  the  pollen  on  the  under  side 
of  the  body  is  transferred  to  the  stigma  of  this  flower. 

Draw  the  flower  from  above,  twice  natural  size. 

Jewel  Weed  {Impatiens  biflora).  —  One  of  the  most  prevalent  of  all  our 


42 


BOTANY 


brookside  flowers  is  the  jewel  weed.  It  well  deserves  its  name,  a  pendent 
flaming  jewel  of  orange. 

The  flower  is  very  irregular  in  shape.  Are  the  flowers  single  or  in  clusters  ? 
The  sepals  as  well  as  the  petals  are  colored.  The  former  are  three  in  num- 
ber, one  of  which  is  saclike  in  shape  and  contracted  at  one  end  into  a  spur. 
The  petals  are  also  three  in  number.  Open  the  flower.  Notice  how  short 
the  filaments  of  the  five  stamens  are.  Make  a  note  of  their  position  with 
relation  to  the  pistil.     Would  self-pollination  be  possible  in  this  flower? 

If  it  is  possible  to  study  jewel  weed  out  of  doors  in  its  native  habitat,  it 
will  be  found  that  humming  birds  are  the  visitors  which  seem  best  adapted 
to  cross-pollinate  the  flower.  A  careful  series  of  observations  by  some  girl 
or  boy  upon  the  cross-pollination  of  this  flower  might  add  much  to  our 
knowledge  regarding  it. 

Jewel  weed  has  the  habit  of  producing  (usually  in  the  fall)  inconspicuous 
flowers  which  never  open  but  which  produce  seeds  capable  of  germination 
and  growth.  Such  flowers  are  said  to  be  deistogamous.  In  England,  where 
the  plant  has  been  introduced,  it  is  found  to  produce  more  deistogamous 
flowers  than  showy  ones,  and  the  showy  ones  do  not  produce  seed.  There 
are  no  humming  birds  in  England,  and  without  this  means  of  pollination 
the  deistogamous  form  prevails.  Make  a  front  view  drawing  of  the  flower 
of  jewel  weed  twice  natural  size. 

Many  other  examples  of  adaptations  to  secure  cross-pollination 
by  means  of  the  visits  of  insects  might  be  given.  The  moun- 
tain laurel;  which  makes  our  hillsides  so  beautiful 
in  late  spring,  shows  a  remarkable  adaptation  in 
having  the  stamens  caught  in  little  pockets  of  the 
corolla.  The  weight  of  the  visiting  insect  on  the 
corolla  releases  the  anther  of  the  stamen  from 
the  pocket  in  which  it  rests,  and  the  body  of  the 
visitor  is  dusted  with  pollen.^ 

The  milkweed  or  butterfly  weed  (Asdepias  cor- 
niiti)  is  another  example  of   a  flower  adapted  to 
insect  pollination.^ 
fl:|  Still  another  example  of  cross-pollination  is  found 

in  the  yucca,  a  plant  somewhat  like  the  Spanish 
bayonet.  In  this  flower  the  stigmatic  surface  is 
above  the  anther,  and  the  pollen  is  sticky  and 
could  not  be  transferred  except  by  insect  aid.  This  is  accom- 
plished in  a  remarkable  manner.     A  little  moth  called  the  Pronuba 

*  See  Hunter  and  Valentine,  Manual,  page  57. 

2  For  an  excellent  account  of  cross-pollination  of  this  flower,  the  reader  is  referred 
to  W.  C.  Stevens,  Introduction  to  Botany.  Orchids  are  well  known  to  botanists  as 
showing  some  very  wonderful  adaptations.  For  simple  reference  reading,  see 
Coulter,  Plant  Relations.  A  classic  easily  read  by  children  is  Darwin,  On  the  Per- 
tilization  of  Orchids. 


Pronuba  pollinat- 
ing pistil  of 
yucca. 


FLOWERS 


43 


Pod  of  yucca  pierced  by 
the  Pronuba. 


gathers  pollen  from  an  anther,  flies  away  with  this  load  to  an- 
other flower,  there  deposits  an  egg  in  the  ovary  of  the  pistil,  and 
then  rubs  its  load  of  pollen  over  the  stigma  of  the  flower.     The 
young  hatch  out  and  feed  on  the  young  seeds 
which  have  been  fertilized  by  the  pollen  placed 
on  the  stigma  by  the  mother.     They  eat  some 
of  the  developing  seeds  and  then  bore  out  of 
the  seed  pod  and  escape  to  the  ground,  leaving 
the  plant  to  develop  the  remaining  seeds  with- 
out molestation. 

The  fig  insect  (Blastophaga  grossorum)  is 
another  member  of  the  insect  tribe  that  is  of 
considerable  economic  importance.  It  is  only 
in  recent  years  that  the  fruit  growers  of  Cali- 
fornia have  discovered  that  the  fertilization 
of  the  female  flowers  is  brought  about  by  a 
gall  fly  which  bores  into  the  young  fruit.^ 

Pollination  by  the  Wind.  —  Not  all  flowers 
are  dependent  upon  insects  for  cross-pollination.  Many  of  the 
earliest  of  spring  flowers  appear  almost  before  the  insects  do. 
These  flowers,  needing  no  conspicuous  colors  or  showy  corolla  to 
attract  insects,  often  lack  this  part  altogether.  In  fact  we  are  apt 
to  entirely  overlook  the  flowers  which  appear  in  the  spring  upon 
our  common  forest  and  shade  trees.  In  many  trees,  as,  for  ex- 
ample, the  willow,  the  flowers  appear  before  the  leaves  come  out. 
Such  flowers  are  dependent  upon  the  wind  to  carry  pollen  from  the 
stamens  of  one  flower  to  the  pistil  of  another.  Most  of  our  com- 
mon trees,  oak,  poplar,  maple,  and  others,  are  cross-pollinated 
almost  entirely  by  the  wind. 

Among  the  adaptations  that  a  wind-pollinated  flower  shows 
are:  (1)  The  development  of  very  many  pollen  grains  to  each 
ovule.  In  one  of  the  insect-pollinated  flowers,  that  of  the  night- 
blooming  cereus,  the  ratio  of  pollen  grains  to  ovules  is  about  eight 
to  one.  In  flowers  which  are  to  be  pollinated  by  the  wind,  a  large 
number  of  the  pollen  grains  never  reach  their  destination  and  are 

*  The  teacher  is  referred  to  Year  Book  of  the  Department  of  Agriculture  for 
1900  for  data  on  the  insect  which  pollinates  the  Smyrna  fig. 


44 


BOTANY 


wasted.  Therefore  in  such  plants  several  thousand;  perhaps 
hundreds  of  thousands  of  pollen  grains  will  be  developed  to 
every  ovule  produced.  Such  are  the  pines.  In  May  and  early 
June  the  ground  under  pine  trees  is  often  yellow  with  pollen, 
and  the  air  may  be  filled  with  the  dust  for  miles  from  the  trees. 
Such,  also,  is  the  case  with  many  of  the  grasses,  the  pollen 
being  produced  in  such  abundance  that  it  causes  a  disease  called 
hay  fever. 

(2)  The  pistil  of  the  flower  is  peculiarly  fitted  to  retain  the 
pollen  by  having  feathery^  projections  along  the  sides  which  in- 


The  staminate  flower  of  the  corn.    Notice  the  hanging  anthers  full  of  pollen. 

crease  the  stigmatic  surface.  This  can  be  seen  in  the  grass.  In 
the  Indian  corn  the  stigmatic  surface  is  thfe  so-called  silk  which 
protrudes  beyond  the  covering  of  modified  leaves  which  form  the 
husk  of  the  ear  of  corn.  All  our  grains,  wheat,  rye,  oats,  and 
others,  have  the  typical  feathery  pistil  of  the  wild  grasses  from 
which  they  descended. 


FLOWERS 


45 


(3)  The  corolla  is  often  entirely  lacking.  It  would  only  be  in  the 
way  in  flowers  that  are  dependent  upon  the  wind  to  carry  pollen. 
Imperfect  Flowers.  —  Some  flowers,  the  wind-pollinated  ones 
in  particular,  are  imperfect.  The  plants  bear  flowers  that  lack 
either  stamens  or  pistils.  In  such  plants,  cross-pollination  must 
of  necessity  follow.  If  the  staminate  flowers  (those  which  con- 
tain only  stamens)  are  developed  on  one  plant  only,  and  the 
pistillate  (those  which  bear  only  pistils)  on  another,  as  in  the 
willow,  we  call  the  plant  dioecious. 
Try  to  make  a  list  of  all  the  trees 
and  grasses  in  your  neighborhood 
that  are  dioecious. 

Other  plants  bear  staminate  and 
pistillate  flowers  on  the  same  plant. 
In  this  case  they  are  said  to  be  mo- 
noecious. The  oak,  hickoiy,  beech, 
birch,  walnut,  and  chestnut  are  fa- 
miliar examples. 

The  pine  tree  is  another  example 
of  monoecious  tree;  the  male  or  staminate  flowers  appear  in  tiny 
clusters  called  catkins,  the  female  or  pistillate  flowers  coming  a 
little  later  as  tiny  cones,  which  in  most  species  of  pines  take 
nearly  two  years  to  mature  into  seeds. 

Water  Pollination.  —  An  unusual  method  of  pollination  is  found 
in  those  plants  which  live  almost  entirely  under  the  water.  In  eel- 
grass  the  pistillate  flowers  are  attached  to  long  slender  stalks  and 
float  on  the  surface  of  the  water.  The  staminate  flowers,  when  ripe, 
break  away  from  their  submerged  stems  and  float  to  the  surface. 
If  these  float  under  a  pistillate  flower,  the  protruding  ends  of  the 
pistils  catch  and  retain  some  of  the  pollen  from  the  staminate 
flower.  Thus  fertilization  follows.  After  pollination,  the  stalk  of 
the  pistillate  flower  coils  up  in  a  spiral  and  draws  the  flower  under 
the  surface  of  the  water,  so  that  the  seeds  may  ripen  in  security. 
Summary.  —  If  we  now  collect  our  observations  upon  flowers 
with  a  view  to  making  a  summary  of  the  different  devices  flowers 
have  assumed  to  secure  cross-pollination,  we  find  that  they  are  as 
follows:  — 


Imperfect  flowers  of  the  squash,  the 
corolla  removed.  Pistillate  flower 
at  the  left. 


46 


BOTANY 


1 

1 

^    , 

1 

^tM^KKb^-y^i^w^M-<^---'-'-^>^--;Si^:-.. 

^■,;.«.>.:;:^v:.;;«.a«-.WW«i«.'    ■ 

^  B 

Flowers  of  the  Lady  Washington  geranium  showing  the  conditions  of  dichogamy;  A,  flower 
with  stamens  ripe,  but  with  the  stigma  not  ready  to  receive  pollen  ;  B,  the  same  flower  at 
a  later  stage ;  the  stamens  have  withered,  but  the  stigma  is  now  ready  to  receive  pollen. 

(1)  The  stamens  and  pistils  may  be  found  in  separate  flowers, 
either  on  the  same  or  on  different  plants. 

(2)  The  stamens  may  produce  pollen  before  the  pistil  is  ready 
to  receive  it,  or  vice  versa.  This  condition  is  called  dichogamy. 
Examples  may  be  found  in  several  of  the  flowers  recommended 
for  study. 

(3)  The  stamens  and  pistils  may  be  so  placed  with  reference  to  each 
other  that  pollination  can  be  brought  about  only  by  outside  assistance. 

In  some  flowers,  as 
is  shown  by  the  prim- 
ula of  our  hothouses, 
the  stamens  and  pis- 
tils are  each  of  two 
different  lengths  in  dif- 
ferent flowers.  Short 
styles  and  long  or  high- 
placed  filaments  are 
found  in  one  flower, 
^    J.  .      ,  ,  ,         .,     and    long  styles  with 

Condition  of  stamens  and  pistils  in  the  spiked  loosestrife  i  i  i 

(.Lythrum  salicaria),  short     01     low  -  placed 


FLOWERS 


47 


filaments  in  the  other.  Pollination  will  be  effected  only  when  some 
of  the  pollen  from  a  low-placed  anther  reaches  the  stigma  of  a  short- 
styled  flower,  or  when  the  pollen  from  a  high  anther  is  placed  upon 
a  long-styled  pistil.  This  can  be  effected  easily  by  flying  insects. 
Flowers  which  have  this  peculiar  condition  are  said  to  be  dimorphic 
(Greek  =  of  two  forms).  There  are,  as  in  the  case  of  the  loosestrife, 
trimorphic  flowers  having  pistils  and  stamens  of  three  lengths. 

Protection  of  Pollen.  —  Pollen,  in  order  to  be  carried  effectively  by 
the  wind,  insects,  or  other  agencies,  must  be  dry.  In  some  flowers 
the  irregular  form  of  the  corolla  protects  the  pollen  from  dampness. 
Other  flowers  close  up  at  night ,  as  the  morning  glory  and  four  o'clock. 
Still  others,  as  the  bell  flower,  droop  during  a  shower  or  at  night. 

Pollen  is  also  protected  from  insect  visitors  which  would  carry  off 
pollen  but  give  the  flower  no  return  by  cross-pollinating  it.  In  some 
flowers  access  of  ants,  plant  lice,  or  other  small  crawling  insects,  to 
the  stamens  is  rendered  difficult  by 
hairs  which  are  developed  upon  the  fila- 
ments or  on  the  corolla.  Sometimes  a 
ring  of  sticky  material  is  found  making 
a  barrier  around  the  peduncle  under- 
neath the  flower.  Many  other  adapta- 
tions of  this  sort  might  be  mentioned. 


Inflorescence.  —  Inflorescence  is  a  term 
given  to  a  flower  cluster.  It  refers  to  the  posi- 
tion of  the  flowers  on  the  flower  stalk.  Sev- 
eral types  of  inflorescence  have  already  been 
noticed.  In  the  Sedum  the  inflorescence  is 
limited  or  the  length  determined  because  the 
flowers  come  out  on  the  ends  of  the  main 
flower  stalk.  Such  a  determinate  inflores- 
cence is  named  a  cyme. 

In  most  flower  clusters  the  inflorescence 
is  said  to  be  indeterminate  because  the  indi- 
vidual flowers  come  out  on  the  sides  of  the 
main  flower  stalk.  Hence  the  length  of  the 
inflorescence  cannot  be  determined.  There 
are  several  common  forms  of  indeterminate 
inflorescence.  Among  forms  we  are  likely 
to  meet  are :  — 


Kaceme  of  moth  mullein. 


48 


BOTANY 


(1)  The  Raceme.  —  Moth  mullein  is  an 
excellent  example.  The  raceme  is  a  tall 
flower  cluster,  bearing  short  pediceled  flow- 
ers along  the  sides  of  its  one  main  stalk.  In 
such  an  inflorescence  you  will  notice  that 
the  oldest  flowers  are  at  the  base  of  the 
cluster.  Notice  another  very  important 
fact,  that  each  flower  comes  out  directly 
over  a  tiny  green  scale  or  leaf.  This  fact 
shows  that  a  flower  cluster  is  a  branch  which 
has  become  changed  or  modified  to  bear 
flowers  instead  of  bearing  only  green  leaves. 

(2)  The  Spike. — A  spike,  as  may  be 
seen  in  figure,  is  simply  a  raceme  in  which 
the  individual  flowers  have  lost  their  pedi- 
cles, the  flowers  coming  out  on  the  main 
flower  stalk.  Examples  are  plantain,  timo- 
thy grass,  and  "butter  and  eggs.'' 

(3)  The  Umbel.  —  In  this  inflorescence 
the  flower  stalks  spring  from  near  the  same 

point  on  the  main  flower  stalk,  like  ribs  in  an  umbrella;  hence  the  name. 
A  flat-topped  cluster,  as  in  wild  carrot  or  the  parsley,  is  the  result. 

(4)  The  Head. — In  the  head  the  long  axis  of  the  inflorescence  is  reduced,  and 
the  flower  pedicles  are  also  absent.    A  compact  cluster,  as  in  clover,  results. 


Spike  of  Linaria  ("butter  and  eggs"). 


An  umbel  of  milkweed. 


Head  of  clover. 


(5)  Composite  Head.  —  This  inflorescence,  so  often  mistaken  for  a  single 
flower,  is  found  only  in  the  great  Composite  family,  to  which  so  many  of  our 
commonest  flowers  and  weeds  belong.  The  daisy,  aster,  golden-rod,  and 
sunflower  are  examples  of  the  Compositae. 

The  composite  head  is  well  seen  in  an  aster  or  the  sunflower.  This  head 
has  an  outer  circle  of  green  parts.  These  parts  look  like  sepals,  but 
in  reality  are  a  whorl  of  bracts.    Taken  together  they  form  an  involiicre. 


FLOWERS 


49 


Inside  the  bracts  are  the  whorls  of  brightly  colored,  irregular  flowers  called 
the  ray  flowers.  They  appear  to  act,  in  some  instances  at  least,  as  an  attrac- 
tion to  insects  by  showing  a  definite  color 
(see  the  common  dogwood,  Cornus  florida). 


A  composite  head. 


Section  through  composite  head,  show- 
ing a  disk  flower  (a),  a  ray  flower  (c), 
and  the  involucre  (rf). 

In  most  cases  the  ray  flowers  are  imperfect. 

Decide  this  in  the  aster  or  cosmos.  (The 
latter  is  easil3'  obtained  in  the  fall  of  the  year.)  Determine  what  parts  of 
the  ray  flower  are  missing.  The  flowers  occupying  the  center  of  the  cluster 
are  the  disk  flowers.  Examine  such  a  flower  under  the  hand  lens.  Deter- 
mine if  the  flower  is  perfect.  A  careful  observer  will  find  in  cosmos  that  the 
anthers  are  united  in  a  ring  around  the  pistil.  This  is  a  typical  condition  in 
the  Compositse. 

Reference  Books'. 

for  the  pupil 

Andrews,  Botany  all  the  Year  Round,  pages  222-236.    American  Book  Company. 
Bailey,  Lessons  uith  Plants,  Part  III,  pages  131-250.    The  Macmillan  Company. 
Coulter,  Plant  Studies.    Chapter  VII.     D.  Appleton  and  Company. 
Dana,  Plants  and  Their  Children,  pages  187-255.     American  Book  Company. 
Hunter  and  Valentine,  Laboratory  Manual  of  Biology.     H.  Holt  and  Company, 
Lea\att,  Outlines  of  Botany,  pages  118-127.     American  Book  Company. 
Lubbock,  Flowers,  Fruits,  and  Leaves,  Part  I.    The  Macmillan  Company. 
Stevens,  Introdvx:tion  to  Botany,  pages  171-206.     D.  C.  Heath  and  Company. 


FOR  THE  TEACHER 

Darwin,  Forms  of  Flowers.      D.  Appleton  and  Company. 

Darwin,  Orchids  Fertilized  by  Insects.     D.  Appleton  and  Company. 

Darwin,  Fertilization  in  the  Vegetable  Kingdom.     Chapters  I.  and  II.     D.  Appletxjn 

and  Company. 
Campbell,  Lectures  on  the  Evolution  of  Plants.    The  Macmillan  Company. 
Gray,  Structural  Botany.     American  Book  Company. 
Lubbock,  British  Wild  Flowers.    The  Macmillan  Company, 
ifear  Book,  U.S.  Department  of  Agriculture,  1896,  1897,  1898,  1899,  1900. 


hunter's    BIOL.  —  4 


V.     FRUITS 


A  Typical  Fruit,  —  the  Pea  or  Bean  Pod.  —  In  the  study  of  the 
flower  of  the  sweet  pea  it  was  seen  that  the  pistil  of  the  flower 
continues  to  grow  after  the  rest  of  the  flower  withers.  If  we 
remove  the  pistil  from  such  a  flower  and  examine  it  carefully, 
we  find  that  it  is  the  ovary  that  has  enlarged.  The  locule  of  the 
ovary  has  become  almost  filled  with  a  number  of  almost  spherical 
bodies,  attached  along  one  edge  of  the  ovary.  These  we  recognize 
as  the  young  seeds. 

Study  of  Bean  or  Pea  Fruit.  — The  pod  of  the  pea  or  string  bean  will  show 
us  these  facts  more  clearly.  Examine,  and  then  draw,  natural  size,  an  un- 
opened pod.  Label 
the  ovary,  peduncle, 
remains  of  style,  stig- 
ma and  calyx  if  you 
can  find  them.  Then 
split  open  the  pod 
and  make  another 
drawing  that  will 
show  the  seeds.  La- 
bel the  stalk  that  at- 
taches each  seed  to 
the  wall  of  the  pod. 
This  is  called  the  fu- 
niculus. That  part 
of  the  oxaxy  wall 
which  bears  the  seeds 
is  the  placenta.  The 
entire  ovary  wall  is 
called  the  'pericarp. 
The  walls  of  the  pod  are  called  valves.  Show  the  above  parts  by  label- 
ing your  drawing. 

The  pod,  which  is  in  reality  a  ripened  ovary  with  other  parts  of  the  pis- 
til attached  to  it,  is  considered  as  a  fruit.  By  definition,  a  fruit  is  a  ripened 
ovary  together  with  any  parts  of  the  flower  that  may  he  attached  to  it.  The  chief 
use  of  the  fruit  to  the  flower  is  to  hold,  to  protect,  and  ultimately  to  dis- 
tribute the  seeds  where  they  can  reproduce  young  plants. 

Formation  of  Seeds. — Each  seed  has  been  formed  as  a  direct  result  of 
the  fertilization  of  the  egg  cell  (contained  in  the  embryo  sac  of  the  ovule) 
by  a  sperm  cell  of  the  pollen  tube. 

Forms  of  Fruits;  the  Achene,the  Simplest  Fruit. — The  forms  taken 
by  fruits  are  very  numerous.     Naturally  the  simplest  of  all  fruits  would  be 

50 


Fruit  of  the  black  locust ;  a  legume,  showing  the  attachment 

of  the  seeds. 


FRUITS 


51 


one  produced  from  a  simple  pistil  or  carpel  containing  only  one  seed.     A 
collection  of  such  fruits  may  be  seen  in  the  ripened  flower  of  the  buttercup, 
smartweed,  or  buckwheat.     A  single  one  of 
these  fruits,  that  is,  a  single  ripe  ovary,  is 
called  an  achene. 

In  the  fruit  of  the  strawberry  the  recep- 
tacle of  the  flower  has  grown  up  to  form  the 
fleshy  mass  that  we  call  fruit,  wliile  the 
achenelike  fruits  are  found  growing  on 
the  outside  of  this.  Such  a  collection  of 
fruits  is  called  an  accessor?/ fruit.     Why? 

Dry  and  Fleshy  Fruits.  —  Fruits  are 
easily  grouped  into  two  great  classes, 
depending  upon  the  amount  of  water 
they  contain  when  ripe.  They  are 
hence  called  dry  or  fleshy. 


The  blackberry ;   a  fruit  made  up 
of  many  separate  ripe  carpels. 


In  the  following  list  decide  which  are  dry  and  which  fleshy  fruits.  Bean, 
apple,  acorn,  orange,  grain  (wheat  or  corn),  pumpkin.  How  would  the  seeds 
in  fleshy  fruit  be  able  to  get  out  of  the  fruit?  What  is  the  use  of  the  fleshy 
part  to  the  fruit? 

Pome.  —  The  botanist  finds  several  kinds  of  fleshy  fruits.  One 
which  we  meet  with  most  frequently  is  called  the  pome.     An 

apple  is  an  excellent  ex- 
ample. 

Study  of  an  Apple.  —  In 
order  to  understand  the  for- 
mation of  the  apple  fruit  it 
will  be  necessary  to  go  back 
to  the  apple  blossom.  This 
gives  us  an  explanation  for 
the  dried  structures  found  at 
the  opposite  end  from  the  ap- 
ple stem.  These  are  the  dried 
ends  of  the  sepals. 

Notice  the  skin.  Of  what 
use  is  it  to  the  fruit?  Re- 
move the  skin  from  the  apple. 
Leave  the  pared  apple  exposed 
to  the  air  a  few  hours.  What 
happens?  The  formation  of 
the  fruit  can  be  understood 
better  if  we  cut  several  see- 
In  a  cross  section  find  the 


Young  apples,  and  apple  blossoms. 


tions  through  it  at  right  angles  to  the  stem.      

locules  of  the  ovary;  how  many  are  there ?    The  tough  walls  directly  mclos- 
ing  the  seeds  are  the  pericarp  or  ovary  wall  proper.     The  fleshy  part  of  the 


52 


BOTANY 


apple,  then,  appears  to  be  formed  from  some  other  parts  of  the  fiower. 

Botanists  are  undecided  as  to  whether  it  is  calyx  tube,  receptacle,  or  part 

of  both  structures.* 

Draw  a  cross  section  of  an  apple  to  show 
the  above  points.  In  a  longitudinal  section 
the  relation  of  the  fruit  to  the  flower  is  better 
shown.  The  stem  was  the  peduncle  of  the 
flower;  the  ovary  wall,  placenta,  and  seeds 
may  easily  be  seen.  In  young  specimens 
the  funiculus,  a  thread  attaching  the  seed 
to  the  placenta,  may  be  found.  A  short 
distance  outside  the  ovary  wall  is  seen  a 
faint  line.  This  is  composed  of  somewhat 
stringlike  structures,  the  tubes  such  as  we 
found  in  the  strings  of  the  string  bean. 
These  bundles  of  ducts  are  called  the  fibro- 
vascular  bundles.  It  is  through  these  ducts 
that  the  apple  has  received  most  of  the 
food  material  which  was  used  to  form  the 
fruit.  We  shall  learn  more  about  the  struc- 
ture of  the  fibrovascular  bundles  in  the  study 
of  the  stems  of  different  plants.     Draw  a 

longitudinal  section  of  the  apple,  natural  size. 

Other  fruits,  built  on  the  same  plan  of  structure  as  the  apple,  are  the 

pear,  quince,  and  hip.    These  fruits  are  classed  as  pomes. 

Pepo.  —  Another  fruit  of  somew^hat  similar  structure  as  the  pome  is  the 
pepo.  The  pumpkin,  gourd,  and  squash  are  examples.  Cut  a  squash  open 
in  cross  sections.     The  ovary  wall  can  be  made  out  close  to  the  numerous 


Longitudinal  section  of  a  pome; 
p,  peduncle;  /,  (ibrovascular 
bundles;  s,  seeds;  pi,  placenta; 
c,  carpel. 


Cross  section  of  a  cucumber.  Note 
the  number  of  locules.  How 
and  where  are  the  seeds  at- 
tached ? 


Cross  section  of  a  green  pepper ; 
a  berry.  How  many  locules 
has  the  ovary?  Note  the  ar- 
rangement of  the  seeds. 


seed  which  fill  the  locules  of  the  ovary.     How  many  locules  are  there  in  the 
squash  ?    The  outer  fleshy  part  and  the  rind  grow  from  the  receptacle  of  the 

'  See  Hvinter  and  Valentine,  Manual,  page  73.  In  this  and  other  suggestions  for 
laboratory  work  it  is  expected  that  the  teacher  will  select  from  the  following  pages 
only  a  portion  of  the  given  material. 


FRUITS 


53 


flowers.     From  what  you  have  observed,  make  up  a  definition  of  a  pepo  fruit. 
Draw  a  cross  section  of  the  squash,  natural  size. 

Berry.  —  A  gardener  or  vegetable  vender  rarely  calls  a  tomato  a  berry. 
Tomatoes,  however,  are  considered  excellent  examples  of  this  type  of 
fruit. ^  In  botanical  language,  a  berry  is  any  pulpy,  juicy  mass  containing 
seeds,  this  mass  inclosed  in  a  rather  tough  but  thin  covering,  as  a  rind  or 
skin.  In  popular  language,  a  berry  is  any  small  round  edible  fruit  con- 
taining small  seeds. 

Drupe.  —  Another  fleshy  fruit 
is  the  drupe  or  stone  fruit.  This 
is  illustrated  by  the  peach  or  cherry. 
In  the  drupe  a  juicy  interior  is  sur- 
^  rounded  by  a  skin;  the  center  of 
the  fruit  is  occupied  by  a  stone 
which  contains  the  seed.  This 
stony  covering  is  made  up  of  the 
inner  wall  of  the  pericarp  (ovary 
wall)  which  has  separated  from  the 
part  which  forms  the  flesh  of  the 
fruit.  The  connection  between 
these  two  layers  is  well  seen  in  a 
clingstone  peach  or  a  very  young 
cherry. 

Classify  as  many  of  the  follow- 
ing named  fruits  as  you  can  :  plum, 
apricot,  egg  plant,  watermelon, 
lemon,  pomegranate,  cranberry, 
black  haw,  pear,  date,  olive.  Make 
up  your  classification  in  tabular 
form.  

T>v  T^       ',  K        ^  r       -J.  The  cherry ;  a  stone  fruit  or  drupe. 

Dry    Fruits.  —  A   dry    iruit 
may  split  open  to  allow  the  escape  of  seeds.    The  pea  is  an  exam- 
ple.    Such  a  fruit  is  said  to  be  dehiscent.^     Study  an  open  pea  pod. 
When  it  splits,  it  separates  along  both  edges  of  the  two  sides  or 
valves.     Such  a  fruit  is  called  a  legume. 

Follicle.  —  If  the  ovary  splits  along  one  edge  of  a  valve  only,  the 
fruit  is  called  a  follicle.     The  milkweed  pod  is  an  example. 

Capsule.  —  When  the  ovary  forming  the  fruit  is  compound,  the 
ovary  having  several  locules,  it  is  said  to  be  a  capsule. 

1  For  laboratory  work  on  the  tomato,  see  Hunter  and  Valentine,  Manual,  page  71. 

2  For  laboratory  exercises  on  dry  dehiscent  fruits,  see  Hunter  and  Valentine, 
Manual,  pages  66,  67,  68. 


54 


BOTANY 


Examine  a  capsule  of  Jimson  weed.  Cut  a  cross  section  and  decide 
how  many  locules  there  are.  Where  is  the  placenta?  How  many  do  you 
find?     Open  a  green  fruit  to  see  the  number  of  seeds  produced.     Draw  the 

cross  section  to  show  the  attach' 
ment  of  the  seeds.  Show  also  the 
method  of  dehiscence  (splitting  of 
capsule) .  How  does  the  fruit  pro- 
vide for  scattering  the  seeds  ? 


SiLiQUE.  —  Attention  is  called 
to  the  two  or  three  odd  types  of 
capsule  frequently  seen.  All  flow- 
ers belonging  to  the  mustard  family 
form  a  silique.  This  differs  from  a 
legume  in  the  presence  of  a  false 
partition  which  divides  the  interior 
into  two  parts.  Another  common 
form  is  the  purse-shaped  capsule; 
it  is  known  as  silicle,  best  seen  in 
the  fruit  of  the  peppergrass  or  of 
the  shepherd's  purse. 


Capsules ;  each  is  made  up  of  five  carpels. 


Indehiscent  Fruits.  —  Among  those  of  most  importance  to  man 
economically  are  the  dry  indehiscent  fruits.  Such  fruits  do  not 
open  to  allow  the  escape  of  seeds.  Among  them  are  found  the 
grainS;  such  as  wheat,  oats,  and  corn.  Many  of  our  most  destruc- 
tive weeds  bear  indehiscent  dry  fruits. 

AcHENE.  — The  simplest  and  commonest  of  all  indehiscent  fruits  is  the 
achene.  This  we  have  seen  before  in  the  buttercup  and  on  the  outside  of 
the  strawberry.  In  many  flowers, 
especially  those  of  the  great  com- 
posite family  (a  group  of  plants 
containing  many  of  the  most  nox- 
ious weeds,  as  the  thistle,  dande- 
lion, sneezeweed,  and  others), 
hairlike  projections  are  developed 
from  the  upper  part  of  the  fruit. 

These  projections  (collectively  called  the  pappus)  are  of  use 

to  the  fruit  because  they  aid  in  carrying  it  to  other  localities 

at  some  distance  from  the  parent  plant. 

Nut.  —  A  nut  can  usually  be  recognized  by  the  hard 

pericarp,  or  ovary  wall,  which  fits  tightly  over  the  kernel. 
Cross  section  of     '^^^  latter,  with  its  covering,  is  the  true  seed.     The  acorn 
a  pecan  nut.       and  pecan  are  good  examples  of  nuts.     The  Brazil  nut  is 


The  acorn,  a  nut  in  which  the  involucre  only 
partly  covers  the  fruit. 


FRUITS 


55 


another  example  of  a  seed  commonly  called  a  nut. 
We  have  to  bear  in  mind  the  distinction  between 
true  nuts  and  hard  seeds.  An  example  of  the  latter 
is  the  horse-chestnut.  Here  the  whole  capsulelike 
structure  is  the  fruit  and  the  "nuts"  are  hard- 
coated  seeds.  On  the  other  hand,  the  acorn  cup  is 
made  up  of  leaflike  structures  which  together  form 
what  is  called  an  involucre.  The  chestnut  bur  is 
another  example  oi  the  involucre  which  has  become 
prickly,  the  nuts  being  each  a  true  fruit. 

Grain.  —  The  grain,  as  we  shall  see  when  we 
study  the  corn  more  carefully,  is  a  fruit  in  which 
the  seed  occupies  most  of  the  space  within  the  fruit, 
and  the  seed  coat  has  become  so  closely  attached  to 
the  ovary  wall  that  the  two  coats  cannot  be  sepa- 
rated. 

Key  Fruit  or  Samara.  —  A  very  common  inde- 
hiscent  fruit  is  found  on  the  maple,  ash,  elm,  and 
other  trees.     It  is  the  key  fruit  or  samara.     In  this 


Grain ;  spikes  of  ripened 
flowers. 


case    the    pericarp  has  lengthened  into  a 
long  wing. 

Hold  a  maple  or  ash  fruit  high  above 
your  head  and  allow  it  to  fall  to  the  ground. 
Does  it  fall  directly  under  the  point  where  it 
was  held  ?  When  and  how  might  the  wings 
be  of  use  to  the  fruit  ?  * 


Key  fruit  of  maple. 


Distinction  between  Seeds  and  Fruits 

—  We  have  seen  that  in  the  case  of 
one-seeded    fruits    it    is    sometimes 
difficult  to  distinguish  between  the   ^^^ 
seed  and  the  fruit.    If  we  are  able    -^ 
to  examine  the  flower  which  forms 
a  certain  fruit,  we  ought  to  have  no 


difficulty  in  making   out  all  of  its  parts.      "^  ^^^Jpi)'^ 
A  cross  section  through  the  ovary  will  show 
us  that  seeds   are   always  surrounded  not 
only  by  seed  coverings,  but  also  by  the  ovary 
wall,  which   later  forms  the  pericarp.     In 


'  For  laboratory  exercises  on  dry  indehiscent  fruits,  see 
Hunter  and  Valentine,  Manual,  pages  69,  70,  74,  75. 


Chestnuts; 
fruits  sur- 
rounded by 
a  prickly  in- 
volucre. 


56  BOTANY 

dehiscent  fruits  the  distinction  between  seed  and  fruit  is  always 
easy.  In  the  indehiscent  fruits  it  is  not  always  so  plain,  espe- 
cially in  the  nuts,  grains,  and  the  achene  fruits.  In  all  of  the 
above  fruits  it  is  necessary  to  remember  that  the  pericarp, 
or  ovary  wall,  adheres  quite  closely  to  the  seed  coat.  In  a 
grain  of  wheat  the  two  have  actually  grown  together.  In  a  nut 
it  is  always  possible  to  scrape  off  the  seed  coat,  as  a  thin 
brownish  covering  around  the  kernel  of  the  nut.  Try  this  with  a 
chestnut. 

Homology  of  Parts  in  Flowers  and  Fruits.  —  In  the  acorn, 
chestnut,  and  hazelnut  a  number  of  leaflike  structures  come  out 
on  the  branch  just  under  the  fruit  and  become  the  capsule  of  the 
acorn,  the  bur  of  the  chestnut,  and  the  husk  of  the  hazelnut 
respectively.  All  these  structures  originate  from  the  same  place 
on  the  branch.  Very  early  in  their  growth  they  appear  to  be 
leaflike.  We  have  reason  to  believe  that  these  structures  are  en- 
tirely similar  to  leaves  in  structure  and  position.  Any  part  of  a 
plant  or  animal  that  has  the  same  position  and  structure  as  an- 
other similar  part  on  another  plant  or  animal  is  said  to  be  homolo- 
gous with  it. 

Homology  of  the  Parts  of  a  Flower.  —  It  is  believed  by  botanists 
that  all  parts  of  a  flower  (sepals,  petals,  stamens,  and  carpels)  are  homolo- 
gous to  each  other  and  also  to  leaves.  It  would  not 
take  a  great  stretch  of  the  imagination  for  you  to  see 
how  like  leaves  are  the  sepals  and  even  the  petals  of 
some  flowers. 

In  roses  and  in  the  water  lily  the  petals  become 
thinner  as  we  go  inward  and  become  tipped  with 
yellow.    On  examination,  this  yellow  tip  is  seen  to  be 
Horizontal  diagram  of      a  pollen  box.     In  short,  the  petal  has  become  a  sta- 

a  lily.    The  central  .  i    •      -^    ^  •  i-  ^  i  i  i. 

area  represents  the  men.     A  very  good  imitation  of  a  pea  pod  could  be 

ovary;     the    bean  made  by  folding  a  pea  leaflet  along  the  midrib.     In 

shaped    structures  ^^^  Sedum  previously  studied  it  will  be  seen  that  the 

the  two  outer  cir-  carpels  bear  the  same  relation  to  the  stamens  as  the 

cles  the  petals  and       stamens  do  to  the  petals.     This  holds  true  of  petals 
sepals,  respectively.  ,  i         t        xi.  i      •         a  i  j.   • 

and  sepals.     In  other  words,  in  a  flower  each  part  in 

each  circle  or  whorl  of  parts  alternates  with  the  parts  of  the  next  succeed- 
ing whorl.  A  glance  at  the  diagram  will  make  this  more  clear.  If  each 
of  the  parts  is  homologous  to  leaves,  then  an  opened  bud  ought  to  help 
make  this  plain. 


FRUITS 


57 


It  becomes  very  evident  after  we  have  studied  a  number  of 
flowers  and  have  then  taken  up  the  fruits,  that  the  same  part  of 
the  flower  almost  invariably  appears  as  a  certain  part  of  the 
fruit,  although  the  part  may  serve  a  very  different  purpose  in  the 
different  fruits.  We  have  already  referred  to  some  examples  of 
this.  Take  as  another  example  the  fate  of  the  ovary  wall  or 
pericarp  in  such  fruits  as  the  peach,  the  apple,  the  pea,  the  nut, 
and  a  key  fruit  of  maple.     In  all  the  above  the  pericarp  of  one 


.rv^ 

Ik  t... 

'^. 

T  CSVMI^^b 

i 

>'-t^^:      *    '      "'?' 

i. 

^y 

h 

r'rP^^'^'^^^ 

m 

ft 

iliitiiii 

W'    iF^^^flR 

rwi!^ 

r^ 

Young  cedars  around  parent  tree.    Photographed  by  Overton. 

is  homologous  with  the  pericarp  in  another.  Yet  what  a  contrast 
between  the  papery  core  of  the  apple  and  the  hard  shell  of  the 
nut,  the  partly  fleshy  and  partly  hard  pericarp  of  the  peach  and 
the  outgrowth  we  call  the  wing  of  the  key  fruit. ^ 

Seed  Dispersal.^  —  If  you  will  go  out  any  fall  afternoon  into 
the  fields,  a  city  park,  or  even  a  vacant  lot,  you  can  hardly 
escape  seeing  how  seeds  are  scattered  by  the  parent  plants 
and   trees.      If    you   count   the    young    maple    seedlings    which 

^  The  teacher  should  point  out  other  homologies  in  flowers  and  fruits.  This 
field  is  one  of  the  richest  in  this  respect  in  all  the  field  of  botany  and  zoology. 

2  At  this  point  a  field  trip  may  well  be  taken  with  a  view  to  finding  out  how 
the  common  fall  weeds  scatter  their  seeds.  Fruits  and  seeds  obtained  upon  this 
trip  will  naake  a  basis  for  laboratory  work  on  the  adaptations  of  seed  and  fruit 
for  dispersal. 


58  BOTANY 

are  growing  directly  under  the  shade  of  the  parent  tree  the  num- 
ber will  surprise  you.  Sometimes  several  hundred  will  be  found 
making  a  brave  start  in  life.  But  nearly  all  these  young  trees 
are  doomed  to  die,  because  of  the  overshading  and  crowding. 
Plants,  like  animals,  are  dependent  upon  their  surroundings  for 
food  and  air.  They  need  light  even  more  than  animals  need  it. 
The  soil  directly  under  the  shade  of  the  old  tree  feeds  the  parent 
and  there  is  no  room  for  the  young  plants.  This  overcrowding  is 
seen  in  the  garden  where  young  beets  or  lettuce  are  growing.  The 
gardener  assists  nature  by  thinning  out  the  young  plants  so  that 
they  may  not  be  handicapped  in  their  battle  for  life  in  the  garden 
by  an  insufficient  supply  of  air,  light,  and  food. 

It  is  evidently  of  considerable  advantage  to  a  plant  to  be  able 
to  place  its  progeny,  which  are  to  grow  up  from  seeds,  at  a  con- 
siderable distance  from  itself,  in  order  that  the  young  plant  may 
be  provided  with  a  sufficient  space  to  get  nourishment  and  foot- 
hold. This  is  the  problem  which  plants  have  to  solve.  Some 
solve  the  problem  to  a  very  much  higher  degree  than  others.  They 
are  the  successful  ones  in  the  battle  of  life. 

Adaptations  for  Seed  Dispersal.  —  Plants  are  fitted  to  scatter 
their  seeds  either  by  having  the  adaptations  in  the  fruit  or  in  the 
seed.  Various  agents,  as  squirrels,  birds,  and  other  animals,  make 
it  possible  for  the  seed  to  be  taken  away  from  the  plant. 

Fleshy  Fruits  with  Hard  Seeds.  —  Fleshy  fruits,  for  example, 
are  eaten  by  animals  and  the  seeds  passed  off  undigested.  Most 
wild  fleshy  fruits  have  either  small,  hard,  indigestible  seeds,  or 
else  they  have  an  unpleasant  flavor. 

Birds  are  responsible  for  much  seed  planting  of  berries  or  other 

small  fruit.     Bears  and  other  berry-feeding  animals  aid  in  this  as 

well. 

Field  Work.  — •  Examine  the  fruit  of  huckleberry,  blackberry,  wild  straw- 
berry, wild  cherry,  black  haw,  wild  grape,  tomato,  currant.  Report  how 
many  of  the  above  have  seeds  with  hard  coatings.  Notice  that  in  most, 
if  not  in  all,  edible  fruits  the  fruit  remains  green,  sour,  and  inedible  until  the 
seeds  are  ripe.     In  the  state  of  nature,  how  might  this  be  of  use  to  a  plant  ? 

Hooks  and  Spines.  —  Some  fruits  possess  hooks  or  spines  which 
enable  the  whole  fruit  to  be  carried  by  animals  or  other  moving 
objects  away  from  the  parent  plant.     Cattle  are  responsible  for  the 


FRUITS 


59 


spread  of  some  of  our  worst  weeds  in  this  way.  The  burdock  and 
clotbur  are  familiar  examples.  In  both  the  mass  of  little  hooks  is  all 
that  remains  of  an  involucre.     Thus  the  whole  fruit  cluster  may 

be  carried  about  and  seeds  scattered. 
In  many  other  fruits  of  the  compos- 
ites, as  in  the  cockleburs  and  beggar's 
ticks,  the  whole  fruits  are  provided 
with  strong  curved  projections  which 
The  cockiebur.  bear  many  smaller  hooklike  barbs. 

Fxamine  the  front  of  a  cockiebur  or  a  beggar's  tick  with  a  low  magnifica- 
tioii  or  even  a  hand  lens.  Draw  such  a  fruit.  Of  what  probable  use  are  the 
many  barbs? 

Pappus.  —  Probably  the  most  important  adaptations  for  dis- 
persal of  seeds  are  those  by  which  the  fruit  is  fitted  for  dispersal 
by  the  wind.  That  much-loved  and  much-hated  weed,  the  dande- 
lion, gives  us  an  example  of  a  plant  in  which  the  whole  fruit,  an 
achene,  is  carried  by  the  wind.  The  parachute,  or  pappus,  is  an 
outgrowth  of  the  ovary 
wall.  Many  other 
fruits,  notably  that  of 
the  Canada  thistle, 
are  provided  with  the 
pappus  as  a  means  of 
getting  away.  If  dan- 
delions are  available, 
notice  the  wonderful 
lightness  and  strength 
of  the  pappus.  In  the 
milkweed  the  seeds 
have  developed  a  silky 
outgrowth  which  may 
carry  the  seeds  for 
miles.  In  New  York 
city  the  air  is  some- 
times full  of  the  down  from  these  seeds  which  is  brought  from 
far  over  the  meadows  of  New  Jersey  by  the  prevailing  westerly 
wind. 


Dandelion  heads;  the  middle  one  a  ma.ss  of  ripe  fruits  ready 
to  be  scattered  by  the  wind.    Photographed  by  Overton. 


GO 


BOTANY 


Winged  Seeds.  —  The  seeds  of  the  pine,  held  underneath  the 
scales  of  the  cone,  are  prolonged  into  wings,  which  aid  in  their 
dispersal. 

Tumble  Weeds.  —  Sometimes  whole  plants  are  carried  by  the 
high  winds  of  the  fall.     This  is  effected  in  the  plants  called  tumble 

weeds,  in  which  the  plant 
body,  as  it  dries,  assumes  a 
somewhat  spherical  shape. 
The  main  stalk  breaks  off  and 
the  plant  may  then  be  blown 
along  the  ground,  scattering 
seeds  as  it  goes,  until  it  is  ulti- 
mately stopped  by  a  fence  or 
bush.  A  single  plant  of  Rus- 
sian thistle  may  thus  scatter 
over  two  hundred  thousand 
seeds. 

Seeds  or  fruits  (for  exam- 
ple, the  cocoanut)  may  fall 
into  the  water  and  be  carried 
thousands  of  miles  to  their  new  resting-place,  the  fibrous  husk 
providing  a  boat  in  which  the  seed  is  carried.  The  great  Eng- 
lish naturalist,  Charles  Darwin,  raised  eighty-two  plants  from 
seeds  carried  in  a  ball  of  earth  attached  to  the  foot  of  a  bird. 
It  is  probable  that  by  means  of  birds  and  water  most  of  the 
vegetation  has  come  into  existence  on  the  newly 
formed  coral  islands  of  the  Pacific  Ocean. 

Some  seeds  have  especial  adaptations  in  the  way 
of  spines  or  projections.  Insects  make  use  of  these 
projections  in  order  to  carry  them  away. 

Ants  plant  seeds  which  they  have  carried  to  their 
nests  for  a  food  supply.  Nuts  are  planted  in  much 
the  same  manner  by  squirrels. 

Explosive  Fruits.  —  Some  fruits  scatter  their  seeds 
through  the  explosion  of  the  seed  case.     Such  a  fruit 
is  the  witch-hazel,  which  explodes  with  such  force  that  the  seeds 
are  thrown  several  feet.     The  wild  geranium,  a  five-loculed  cap- 


Cross  section  of  a  cocoanut  in  its  fibrous  husk. 


Pod  of  crane's 
bill  discharg- 
ing its  seed. 


FRUITS 


61 


sule,  splits  along  the  edge  of  each  locule,  snaps  back,  and  throws 
the  seed  for  some  distance.  Jewel  weed  fruits  burst  open  in  some- 
what the  same  manner.  Make 
observations  on  jewel  weed  to 
find  out  if  possible  how  the  ex- 
plosion of  the  fruit  is  caused. 

Large  Numbers  of  Seeds.  — ■ 
Plants  which  do  not  have  espe- 
cial means  for  scattering  their 
seeds  may  make  up  for  this  by 
producing  a  large  number  of 
seeds  and  holding  them  in  pod- 
like fruits  which  are  easily 
shaken  by  the  wind.  The  poppy 
and  jimson  weed  are  familiar 
examples  of  such  plants.  Each 
capsule  of  jimson  weed  contains 
from  four  hundred  to  six  hun- 
dred seeds,  depending  upon  its 
size.  If  all  of  these  seeds  de- 
veloped, the  whole  earth  would 
soon  be  covered  with  jimson  weed,  to  the  exclusion  of  all  other 
forms  of  plant  life.  That  this  is  not  the  case  is  due  to  the  fact 
that  only  those  seeds  which  are  advantageously  placed  can  de- 
velop; the  others  will,  for  various  reasons  (lack  of  moisture  to 
start  the  young  seed  on  its  way,  poor  soil,  lack  of  air  or  sunlight, 
overcrowding),  fail  to  germinate. 

The  Struggle  for  Existence.  —  Those  plants  which  provide  best 
for  their  young  are  usually  the  most  successful  in  life's  race. 
Plants  which  combine  with  the  ability  to  scatter  many  seeds  over 
a  wide  territory,  the  additional  characteristics  of  rapid  growth, 
resistance  to  dangers  of  extreme  cold  or  heat,  attacks  of  parasitic 
enemies,  inedibility,  and  peculiar  adaptations  to  cross-pollination 
or  self-pollination,  are  usually  spoken  of  as  weeds.  They  flourish 
in  the  sterile  soil  of  the  roadside  and  in  the  fertile  soil  of  the 
garden.  By  means  of  rapid  growth  they  kill  other  plants  of 
slower  growth  by  usurping  their  territory.     Slow-growing  plants 


Wild  geranium  (crane's bill),  showing  method 
of  seed  dispersal;  a,  flower  with  seeds 
nearly  ripe;  b,  flower  with  seeds  ripe; 
c,  flower  after  having  thrown  seeds.  (After 
Lubbock.) 


62 


BOTANY 


are  thus  actually  exterminated.  Many  of  our  common  weeds 
have  been  introduced  from  other  countries  and  have,  through 
their  numerous  adaptations,  driven  out  other  plants  which 
stood  in  their  way.  It  is  evident  that  the  plants  which  are  best 
adapted  to  changes  in  their  surroundings,  those  plants  which 
have  allowed  themselves  to  be  molded  to  fit  into  new  conditions, 
are  the  successful  ones.  Such  is  the  Russian  thistle.  First  in- 
troduced from  Russia  in  1873,  it  spread  so  rapidly  that  in  twenty 
years  it  had  appeared  as  a  common  weed  over  an  area  of  some 
twenty-five  thousand  square  miles.  It  is  now  one  of  the  greatest 
pests  in  our  Northwest. 

Economic  Value  of  Fruits.  —  Our  grains  are  the  cultivated  progeny  of 
wild  grasses.     Domestication  of  plants  and  animals  mark  epochs  in  the 


^ — ^_ 


CORN         "^ 


640  to  3200  bushels  per  sauare  mile  \ 


\oyer3ZOO 


10 


H 


ie_ 


Indian  Corn  Production— Percentage 


^A 


40 


i^ 


60 


JL 


80 

1 


iL 


-A 


m^ 


I 


Illinois 


Lowa 


Neb.        Mo.     Kan.  Ohio  Ind.  Tex.        Rest  of  United  States 


advance  of  civilization.  The  man  of  the  stone  age  hunted  wild  beasts  for 
food,  and  lived  like  one  of  them  in  a  cave  or  wherever  he  happened  to  be ; 
he  was  a  nomad,  a  wanderer,  with  no  fixed  home.  The  tribes  which  first 
cultivated  the  soil  made  a  great  step  in  advance,  for  they  had  as  a  result  a 


FRUITS 


63 


fixed  place  for  habitation.  The  cultivation  of  grains  and  cereals  gave  them 
a  store  of  food  which  could  be  used  at  times  when  other  food  was  scarce. 
The  word  cereal  (derived  from  Ceres,  the  Roman  Goddess  of  Agriculture) 
shows  the  importance  of  this  crop  to  Roman  civilization.  From  earliest 
times  the  growing  of  grain  and  the  progress  of  civilization  have  gone  hand 
in  hand.  As  nations  have  advanced  in  power,  their  dependence  upon  the 
cereal  crops  has  been  greater  and  greater. 

"  Indian  corn,"  says  John  Fiske,  in  The  Discovery  of  America,  "  has  played 
a  most  important  part  in  the  discovery  of  the  New  World.     It  could  be 


-^^ 


/    ^ 


i  "%. 


WHEAT     \ 

/60  to  640  bushels  per  sauare  mile  '\ 

over    640        »  «         „         . 


't 


Wheat  Crop  in  United  States — Percentage  Source 

20  30  40  50     M  7,0 


30  90 


Minnesota      Kansas  N. Dak.  S. Dak.  Neb.    O.  Cal.Ind.Mo.Pa. 


Other  States 


planted  without  clearing  or  plowing  the  soil.  There  was  no  need  of  thresn- 
ing  or  winnowing.  Sown  in  tilled  land,  it  yields  more  than  twice  as 
much  food  per  acre  as  any  other  kind  of  grain.  This  was  of  incalculable 
advantage  to  the  English  settlers  in  New  England,  who  would  have  found  it 
much  harder  to  gain  a  secure  foothold  upon  the  soil  if  they  had  had  to  begin 
by  preparing  it  for  wheat  or  rye." 

To-day,  in  spite  of  the  great  wealth  which  comes  from  our  mineral 
resources,  live  stock,  and  manufactured  products,  the  surest  index  of  our 
country's  prosperity  is  the  size  of  the  wheat  and  com  crop.  According  to 
the  last  census,  the  amount  of  capital  invested  in  agriculture  was  over 
twenty  billion  dollars,  while  that  invested  in  manufactures  was  less  than 
one  half  that  amount. 


64 


BOTANY 


Corn.  —  Two  billion  six  hundred  and  sixty-six  million  four  hundred 
forty  thousand  two  hundred  and  seventy-nine  bushels  of  corn  were  raised 
in  the  United  States  during  the  year  1900.  This  figure  is  so  enormous  that 
it  has  but  little  meaning  to  us.  In  the  past  half  century  our  corn  crop  has 
increased  over  350  per  cent.  Illinois  and  Iowa  are  the  greatest  corn-pro- 
ducing states,  each  having  a  yearly  record  of  over  four  hundred  million 
bushels.  The  figure  on  page  62  shows  the  principal  corn-producing 
areas  in  the  United  States. 


^ — __ 


COTTON 

t>yS]  I  to  20  bales  persauare  mile 


I  over 20   . 


Cotton  Crop  in  United  States — Percentage  Source 


JL 


40 


5.0 


60 

i_ 


7.0 


GO 


9.0 


Texas 


Georgia 


Miss.       Alabama    S.Car.    Ark.      La.    N.C.Other  States 


Percentage  Consumption — United  States  Cotton  Crop 

20  30  40  50  60  7,0  80  9.0 


10 


United  States 
North  South 


Great  Britain  &  Ireland 


Germany       France  It.  Rst.Wld, 


Indian  corn  is  put  to  many  uses.  It  is  a  valuable  food.  It  contains 
a  large  proportion  of  starch,  from  which  glucose  and  alcohol  are  made. 
Machine  oil  and  soap  are  made  from  it.  The  leaves  and  stalk  are  an  excel- 
lent fodder;  they  can  be  made  into  paper  and  packing  material.  Mat- 
tresses can  be  stuffed  with  the  husks.  The  pith  is  used  as  a  protective 
belt  placed  below  the  water  line  of  our  huge  battle  ships.  Corn  cobs  are 
used  for  fuel,  one  hundred  bushels  having  the  fuel  value  of  a  ton  of  coal. 

Wheat.  — Wheat  is  the  crop  of  next  greatest  importance  in  size,  and  is 


FRUITS  65 

of  even  greater  money  value  to  this  country.  Nearly  six  hundred  and  sixty 
miUion  of  bushels  were  raised  in  this  country  in  1900,  representing  a  total 
money  value  of  $  500,000,000.  Seventy-two  per  cent  of  all  the  wheat  raised 
comes  from  the  North  Central  States  and  California.  About  three  fourths 
of  the  wheat  crop  is  exported,  nearly  one  half  of  it  to  Great  Britain.  Wheat 
has  its  chief  use  in  its  manufacture  into  flour.  This  forms  the  chief  industry 
of  Minneapolis,  Minnesota,  and  several  other  large  and  wealthy  cities  in  this 
country.  The  germ,  or  young  wheat  plant,  is  sifted  from  the  flour  and 
made  into  breakfast  foods. 

Other  Fruits.  —  Of  the  other  grain  and  cereals  raised  in  this  country, 
oats  are  the  most  important  crop.  Hay  as  a  fodder  crop  is  of  great  value 
next  to  that  of  corn,  nearly  $500,000,000  worth  being  raised  every  year. 
Buckwheat,  barley,  and  rye  are  also  raised  in  considerable  amounts,  but  are 
relatively  unimportant  commercially.  Among  our  fruits  cotton  is  probably 
that  of  the  most  importance  to  the  outside  w^orld.  Over  ten  million  bales 
of  five  hundred  pounds  each  are  raised  annually.  Of  this  amount  a  large 
amount  is  exported,  the  United  States  producing  over  three  fourths  of 
the  world's  cotton  supply.  The  relation  of  source  and  distribution  of  the 
cotton  crop  can  be  seen  by  a  glance  at  the  accompanying  diagram. 

Other  important  fruit  crops  might  be  mentioned.  There  are  over  one 
hundred  and  seventy-five  million  bushels  of  apples  produced  every  year  in 
the  United  States.  Pears,  peaches,  plums,  cherries,  and  grapes  play  an 
important  part  in  the  crop,  especially  in  California,  which  produces  yearly 
over  seven  hundred  million  pounds  of  grapes,  over  fifty  per  cent  of  the  total 
yield  in  the  United  States. 

Reference  Books 

for  the  pupil 

Dana,  Plants  and  Their  Children,  pages  27-49.     American  Book  Company. 
Goff  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chap.  XXIII.     Ginn  and  Company. 
Bailey,  Lessons  with  Plants,  pages  251-314.     The  Macmillan  Company. 
Bailey,  Botany,  Chaps.  XXI,  XXII.     The  Macmillan  Company. 
Coulter,  Plant  Studies,  Chap.  VI.     D.  Appleton  and  Company. 
Beal,  Seed  Dispersal.     Ginn  and  Company. 
Newell,  Reader  in  Botanij,  pages  97-137.     Ginn  and  Company. 

FOR   THE    TEACHER 

Bailey,  The  Evolution  of  our  Native  Fruits.     The  Macmillan  Company. 
Bailey,  Plant  Breeding.     The  Macmillan  Company. 
Hodge,  Nature  Study  and  Life,  Chaps.  X,  XI.     Ginn  and  Company. 
Sargent,  Corn  Plants.     Houghton,  Mifflin,  and  Company. 

Kerner  (translated  by  Oliver),  Natural  History  of  Plants.      Henry  Holt  and  Com- 
pany.    4  Vols.     Vol.  II,  Part  2. 
hunter's   BIOL.  —  5 


VI.    SEEDS  AND  SEEDLINGS 

Relation  of  Flower  to  Fruit.  —  We  have  already  found  in  our 
study  of  the  fruit  that  the  bean  pod  is  a  direct  outgrowth  from 
the  flower.  It  is,  in  fact,  the  ovary  of  the  flower,  with  the  parts  im- 
mediately surrounding  it,  which  has  grown  larger  to  make  a  fruit. 

Use  of  Fruit.  —  The  fruit  is  the  most  important  result  of  the 
flower.  It  holds  and  protects  the  seeds  until  the  time  comes  that 
they  are  able  to  germinate  and  produce  new  plants  like  the  original 
plant  from  which  they  grew. 

Study  of  a  Bean.  —  Let  us  now  take  up  the  careful  study  of  a  bean  in  order 
better  to  understand  how  the  seed  may  produce  a  young  plant.  For  this 
purpose  we  need  some  dry  pods  of  the  string  bean  and  some  kidney  beans. ^ 

If  we  have  already  studied  the  pod  of  the  bean,  it  will  now  be  easy  for  us 
to  find  and  identify  the  parts  of  the  pod  which  were  style,  stigma,  and  ovary 
in  the  flower.  Opening  the  pod  along  one  of  the  edges  or  sutures  of  the  two 
valves,  we  find  the  seeds  fastened  to  the  placenta  each  by  the  little  stalk  or 
funiculus.  If  we  pull  a  single  bean  from  its  attachment,  we  find  the  funicu- 
lus leaves  a  scar  on  the  coat  of  the  bean;  this  scar  is  called  the  hilum.  Look 
near  the  hilum  for  a  tiny  hole  called  the  micropyle.  (Do  not  confuse  it  with  a 
little  knob  called  the  strophiole.)  Turn  back  to  the  figure  showing  the 
ovule  ui  the  ovary.  Find  there  the  little  hole  through  which  the  pollen 
tube  reached  the  embryo  sac.  This  hole  is  called  the  micropyle,  and 
is  identical  with  the  micropyle  in  the  seed.  Draw  a  single  kidney  bean  from 
the  edge  bearing  the  hilum  scar,  and  show  exactly  the  location  of  the  hilum, 
micropyle,  and  strophiole.     Make  the  drawing  twice  natural  size. 

Home  Experiment.  —  Divide  ten  kidney  beans  of  nearly  equal  size  into 
two  lots.  Cover  the  micropyles  of  one  lot  with  wax  or  vaseline,  weigh 
both  lots  of  seeds  exactly,  then  leave  them  in  water  over  night.  Weigh 
both  lots  in  the  morning.  Note  any  differences  in  the  appearance  of  the 
two  lots  of  seeds.  What  is  one  use  of  the  micropyle  to  the  bean  seed? 
This  experiment  may  be  made  more  instructive  by  covering  a  third  lot  of 
beans  completely  with  wax  and  exposing  them  to  the  same  conditions  as 
you  did  the  others.  Does  any  water  get  in  through  the  seed  coats? 
Remove  carefully  the  coat  from  a  kidney  bean  which  has  been  soaked  over 
night  in  water.  This  coat,  because  of  its  toughness,  is  called  the  testa.  Do 
you  find  another  coat  under  it?  You  find  the  bean  separates  into  two 
parts;  these  are  called  the  cotyledons.  If  you  separate  the  cotyledons  very 
carefully,  you  find  certain  other  structures  between  them.  The  rodlike 
part  is  called  the  hypocotyl  (meaning  under  the  cotyledons).  This  will  later 
form  the  root  (and  part  of  the  stem)  of  the  young  plant.     Look  for  the  first 

*  For  extended  laboratory  study  on  the  bean,  see  Hunter  and  Valentine,  Manualf 
page  13. 

66 


SEEDS  AND  SEEDLINGS  67 

true  leaves  folded  together  between  the  cotyledons.  How  many  leaves 
are  there  ?  That  part  of  the  plant  above  the  cotyledons  is  known  as  the 
-plumule  or  epicotyl  (meaning  above  the  cotyledons) .  Later  we  shall  wish  to 
know  what  part  of  the  future  plant  the  epicotyl  forms. 

All  the  parts  of  the  seed  within  the  seed  coats  together  form  the  embryo 
or  young  plant. 

Draw  the  bean  to  show  all  the  above  parts,  twice  natural  size.  Label 
every  part  carefully. 

Food  in  the  Cotyledons.  —  The  problem  now  before  us  is  to  find 
out  how  the  embryo  of  the  bean  is  adapted  to  grow  into  an  adult 
plant.  Up  to  this  stage  of  its  existence  it  has  had  the  advantage 
of  food  and  protection  from  the  parent  plant.  Now  it  must  begin 
the  battle  of  life  alone.  We  shall  find  in  all  our  work  with  plants 
and  animals  that  the  problem  of  food  supply  is  always  the  most 
important  problem  to  be  solved  by  the  growing  organism.  Let 
us  see  if  the  embryo  is  able  to  get  a  start  in  life  (which  many 
animals  get  in  the  egg)  from  food  provided  for  it  within  its  own 
body. 

Experiment.  —  Mash  up  a  little  piece  of  a  bean  cotyledon  which  you 
have  previously  soaked  in  water.  Test  for  starch  with  iodine  solution 
What  color  appears?  If  you  now  mount  a  little  of 
the  stained  material  in  water  on  a  glass  slide  under 
the  compound  microscope,  you  will  find  that  the 
starch  is  contained  in  the  form  of  little  ovoid  bodies 
called  starch  grains.  The  starch  grains  and  other 
food  products  are  made  use  of  by  the  growing  plant 
in  a  manner  which  we  shall  later  know  more  about. 

Test  the  cotyledon  of  a  bean,  for  proteid  food, 
with  nitric  acid  and  ammonium  hydrate.  The  change 
of  the  color  of  the  surface  shows  us  that  considerable 
proteid  is  present.  According  to  the  compilations 
from  the  government  reports,  the  kidney  bean  is  one 
of  the  materials  very  rich  in  proteid  food.  It  con-  Starch  grains  in  the  cells 
tains  not  less  than  23  per  cent  of  proteid,  57  per  cent  of  a  potato  tuber, 

of  carbohydrates,  and  about  2  per  cent  of  fats. 

Test  a  bean  by  heating  it  on  a  piece  of  paper  in  the  oven  to  see  if  the 
small  quantity  of  oil  present  can  be  detected  by  this  means. 

The  above  tests  show  us  that  the  bean  seed  contains  a  large 

supply  of  food  which,  as  we  shall  see,  is  used  by  the  young  plant 

in  its  germination. 

Germination  of  the  Bean,  Pea,  and  Com.  — Soak  the  seeds  at  least  eight 
hours  in  water  before  planting.  In  general,  the  larger  the  seed  the  longer 
the  immersion  in  water  before  planting.  For  use  in  the  laboratory  seeds 
may  be  planted  in  shallow  boxes  or  trays.  Use  sawdust,  clean  white 
sand,  or  sphagnum  moss  to  plant  them  in.  Make  holes  in  the  bottom  of  the 
boxes  for  drainage.     Plant  beans  about  half  an  inch  deep;  smaUer  seeds 


68 


BOTANY 


may  be  planted  from  five  to  ten  times  their  own  depth.  Keep  ths  tem- 
perature as  near  75°  Fahrenheit  as  possible.  Protect  at  night  from  sudden 
drops  in  temperature  by  careful  covering  of  the  young  plants.  Water 
regularly  and  moderately.  If  the  material  for  class  work  is  ready  at  cer- 
tain stages  before  time  to  use  in  the  laboratory,  the  specimens  may  be  placed 
in  4  per  cent  formol  solution  until  needed.  After  the  different  plants  have 
appeared  above  ground  a  daily  record  should  be  made  of  at  least  one  of 
each  kind  of  seed  or  grain  planted.  ]Note  the  length  of  time  it  took  each 
to  appear  above  the  ground  and  make  daily  drawings  until  the  young  plants 


Sprouting  beans.    Note  the  arch  in  the  hypocotyl. 

in  its  growth  ? 


How  is  this  of  ';^e  to  the  plan* 


are  at  least  two  weeks  old.  At  the  end  of  that  time  an  entire  plant  of  bean, 
pea,  and  corn  should  be  removed  and  drawn.  You  will  thus  accurately 
determine  the  fate  of  each  part  of  the  growing  plant. 

Answer  the  following  questions  from  bean  seedlings  grown  at  home  or  from 
material  supplied  you  in  the  laboratory.  Which  part  of  the  embryo  breaks 
through  the  seed  coats  first  and  at  what  point  does  it  appear  ?  In  what 
direction  does  the  hypocotyl  grow?  Does  it  always  take  this  direction? 
How  does  the  seedling  break  through  the  ground?  Which  part  appears 
first  above  ground?  Why  does  it  assume  this  position?  Are  the  cotyle- 
dons pushed  or  pulled  out  of  the  ground  ?  What  color  has  the  plant  above 
ground?  What  becomes  of  the  cotyledons  in  old  specimens?  Pleasure  the 
cotyledons  in  a  young  specimen  and  then  again  when  the  plant  has  grown 
older.  Do  they  grow  in  size?  Make  a  table  which  shows  the  ultimate  fate 
in  a  bean  seedhng  of  the  following  parts-  cotyledons,  hypocotyl,  epicotyl. 


SEEDS  AND  SEEDLINGS 


69 


Make  a  series  of  at  least  three  drawings  of  the  developing  seedling  to  show 
the  growth  of  the  various  organs  In  this  series  draw  a  line  across  your 
paper  to  show  the  level  of  the  ground. 

Problems  cf  Growth'  —  There  are  several  interesting  problems  concerning 
the  growth  of  the  bean  seedling.  Most  of  these  questions  we  can  solve 
with  the  aid  of  simple  experiments. 
These  experiments  may  bo  allotted 
to  different  meml)ers  of  the  class 
to  perform  at  home  and  bring  to 
school  when  the  laboratory  work 
of  the  bean  seedling  is  finished  and 
the  pupils  are  ready  for  a  discus- 
si  L.n  of  its  growth.  The  following 
experiment  should  be  started  at 
once. 

Experiment.  —  What  is  the  func- 
tion oj  the  cotyledons  of  the  bean? 
Plant  six  beans  in  sawdust.  After 
they  have  grown  so  that  the  hypo- 
cotyls  are  above  the  surface,  re- 
move the  cotyledons  from  three 
beans.  Watch  the  growth  of  both 
lots  very  carefully,  making  sure 
that  they  are  exposed  to  exactly 
the  same  conditions  of  heat,  mois- 
ture, light,  and  air.  After  two 
weeks  draw  a  bean  from  each  lot. 
Of  what  use  to  the  growing  plant 
are  the  cotyledons?     Why?^ 


'mm 


Bean  seedlings.  Note  that  in  the  older  seed- 
lings to  the  left  the  cotyledons  have  been 
almost  entirely  used  up. 


Germination.  —  All  the  stages 
passed  through  by  the  youjig 
plant,  from  the  time  the  seed 
begins  to  sprout  until  it  can 
take  care  oj  itself  by  means  of  its  roots  and  leaves,  are  known  as  the 
stages  of  germinatioii.  The  young  plant  ceases  to  be  a  seedling  after 
it  has  lost  its  seed  leaves  or  cotyledons. 

A  comparison  of  the  Pea  and  Bean.  —  Suggestions  for  laboratory  work. 
Compare  the  markings  on  the  outside  of  the  pea  with  those  you  found  on 
the  bean.  Make  a  diagram  of  the  pea  drawn  from  the  hilum  end.  Show 
the  following  structures  neatly  labeled  :  hilum,  micropyle,  strophiole. 

Open  a  soaked  seed.     How  many  cotyledons  do  you  find? 

Plants  having  two  cotyledons  or  seed  leaves  are  called  dicotyledons.  Do 
you  know  any  other  plants  having  two  cotyledons  besides  the  pea  and  bean  ? 

*  At  this  point,  experiments  may  be  introduced,  showing  the  result  of  oxidation, 
of  organic  materials,  the  tests  for  carbon  dioxide,  the  fact  that  oxidation  of  food 
substances  takes  place  within  the  growing  pea  or  bean  (as  shown  bj^  placing  ger- 
minating seeds  within  a  closed  jar),  and  that  air  is  necessary  for  germination. 

2  It  must  be  remembered  that  this  is  not  quite  a  fair  test  to  the  bean,  because  we 
take  away  from  the  young  plant  part  of  its  own  body. 


70 


BOTANY 


Most  of  our  trees,  and  vevy  many  of  our  common  plants,  belong  to  this 
great  group  of  plants. 

How  many  of  the  parts  inside  the  cotyledons  can  you  identify  and  com- 
pare with  similar  structures  in  the  bean?      Look  for  hypocotyl,  epicotyl, 

and  true  leaves.  Are  the  structures 
named  homologous  with  the  same 
structures  in  the  bean?  How  do 
3'ou  know? 

Draw  the  pea,  showing  all  the 
above-named  parts. 

Compare  the  pea  seedling  and 
bean  seedling  with  regard  to  the 
following  points:  (1)  as  to  the 
method  of  getting  out  of  the  ground; 
(2)  as  to  the  part  which  appears 
first;  (3)  as  to  the  parts  that  ap- 
pear above  ground ;  (4)  the  ultimate 
fate  of  each  part. 

This  must  be  made  the  subject 
of  an  extended  home  experiment. 
Drawings  should  be  made  to  illus- 
trate each  stage  of  growth,  and  each 
part  should  be  carefully  labeled.^ 

An  experiment  to  prove  the  func- 
tion of  the  cotyledons  of  the  pea 
may  be  made  in  very  much  the 
same  way  as  the  experiment  per- 
formed to  find  out  the  same  thing 
for  the  bean.  This  experiment  can 
be  made  at  home  and  brought  in 
at  the  same  time  as  the  bean  ex- 
periment, and  comparisons  made. 


Experiment  to  show  the  function  of  the  coty- 
ledons of  the  pea,  photographed  at  the 
end  of  two  weeks.  Note  the  size  of  the 
plants  at  the  left,  without  cotyledons. 


Analogy.  —  A  structure  which  has  the  same  function  or  use  as 
another  structure  is  said  to  be  analogous  to  it.  Is  the  cotyledon  of 
the  pea  analogous  to  the  cotyledon  of  the  bean  ?  Is  it  also  ho- 
mologous? 

Cotyledons  as  Foliage  Leaves.  —  In  the  young  plants  which  we 
have  just  been  talking  about,  the  cotyledons  hold  a  reserve  food 
supply,  but  do  not  serve  at  any  time  as  true  leaves  for  the  plant 
In  many  dicotyledons,  however,  the  seed  leaves  do  act  as  true 
leaves.  This  may  well  be  seen  in  the  squash  seedling.  Here  the 
young  plant  has  little  or  no  food  stored  in  the  cotyledons;  it 
must  be  prepared  to  take  care  of  itself  quickly.  It  does  this  by 
means  of  the  rapidly  growing  cotyledons,  which  soon  unfold  as 
true  leaves  to  the  sun.  In  the  seeds  of  the  pea  and  bean  we  have 
found  that  the  embryo  takes  up  all  the  space  within  the  seed 

^  See  Hunter  and  Valentine,  Manual,  page  18. 


SEEDS   AND  SEEDLINGS 


71 


coats.     There   are   some   dicotyledonous   plants   that   have   food 
stored  outside  of  the  embryo.     Such  a  plant  is  the  castor  bean.^ 

Castor  Bean.  —  A  section  cut  vertically  through  the  castor  bean  discloses 
a  white  oily  maes  directly  under  the  seed  coats.  This  mass  is  called  the 
endosperm.  If  it  is  tested  with  iodine,  it  can  be  proved  to  contain  starch; 
oil  is  also  present  in  considerable  quantity  Within  the  endosperm  lies  the 
embryo,  a  thin,  whitish 
structure.  If  the  embryo 
is  carefully  removed  from 
the  endosperm  (see  direc- 
tions in  preparation  note, 
page  19,  Hunter  and  Val- 
entine, Manual), the  struc- 
ture of  the  embryo  can 
easily  be  made  out. 

Open  a  number  of 
soaked  seeds  of  the  fol- 
lowing-named plants,  and 
locate,  with  the  aid  of  the  diagrams,  the  embryo  and  the  endosperm  in  each: 
four  o'clock,  morning  glory,  castor  bean,  maple.  Make  diagrams  for  your 
notebook  to  show  these  facts. 


Arrangement  of  embryo  in  endosperm  (Gray)  ;  a,  morn- 
ing glory;  b,  barberry;  c,  potato;  d,  four  o'clock. 


A  cornfield,  showing  staminate  and  pistillate  flowers. 

The  Corn.  —  The  ear  of  corn  is  not  a  single  fruit,  but  a  large 
number  of  fruits  in  a  cluster,  like,  for  example,  a  bunch  of  bananas. 

1  For  laboiatory  work  on  the  castor  bean,  see  Hunter  and  Vah^ntine,  Manual, 
page  19. 


72 


BOTANY 


Push  back  the  husk  of  a  young  ear  of  corn.  The  husk  is  simply 
a  covering  of  leaflike  parts  which  has  grown  over  the  young 
fruits  for  their  better  protection.     We  have  already  noticed  such 

a  structure  forming  the  capsule  of  the  acorn 
and  bur  of  chestnut.  What  did  we  call  it  ? 
We  uncover  what  was  a  short  time  before 
a  bunch  of  ver}^  peculiar  flowers.  The  corn 
cob  is  the  much-thickened  flower  stalk  on 
which  the  flowers  were  clustered.  If  you 
have  removed  the  husk  carefully  you  will 
see  part  of  each  flower  remaining  attached 
to  each  grain  of  corn.  The  so-called  silk  of 
corn  is  nothing  more  than  a  long  central 
style  and  stigma.  The  corn  grain  itself  was 
also  part  of  the  flower  —  the  same  part 
that  formed  the  pod  of  the  bean  with  its 
contained  seeds.  The  corn  grain,  therefore, 
is  a  fruit  and  not  a  seed.  Is  the  grain  of 
corn  homologous  with  the  pea  or  bean? 

Laboratory  Suggestions  for  Work  on  Grain  of 
Corn?  —  In  a  single  grain  of  corn  which  has  been 
soaked  at  least  twenty-four  hours,  notice  the  differ- 
ences between  the  attached  and  free  ends  of  the 
grain.  Look  for  the  scar  which  marked  the  at- 
tachment of  the  silk.  The  light-colored  area 
found  on  one  surface  marks  the  position  of  the 
embryo ;  the  rest  of  the  grain  contains  the  endo- 
sperm. Cut  a  grain  perpendicular  to  the  flat  side 
of  the  grain  in  a  lengthwise  direction.  Find  the 
embryo  from  its  relation  to  the  outside  of  the 
grain.  Apply  a  drop  of  weak  iodine  solution. 
What  material  is  found  in  the  endosperm  of  corn  ? 
The  part  of  the  grain  that  does  not  stain  so 
deeply  with  iodine  is  the  embryo.  Find  two  parts, 
—  a  tiny  elongated  structure  and  an  area  lying  be- 
tween it  and  the  endosperm.  The  latter  is  the 
single  cotyledon. 

Use  a  lens.  Notice  that  the  elongated  struc- 
ture in  the  embryo  has  two  parts,  the  hypocotyl 
pointing  toward  the  attached  end  and  the  plumule  or  the  epicotyl  point- 
ing toward  the  unattached  end. 

Draw  the  longitudinal  section  of  the  corn  grain  as  seen  stained  with 
iodine.     Mark  all  the  parts.     Make  your  drawing  at  least  twice  natural  size. 


Longitudinal  section  of 
young  ear  of  corn ;  O,  the 
fruits;  S,  the  stigmas; 
SH,  sheathiike  leaves; 
ST,  the  flower  stalk  or 
peduncle.  (After  Sar- 
gent.) 


'  See  Hunter  and  Valentine,  Manual,  page  16. 


SEEDS  AND  SEEDLINGS  73 

Endosperm  the  Food  Supply  of  Corn.  —  We  do  not  find  that  the 
one  cotyledon  of  the  corn  grain  serves  the  same  purpose  to  the 
young  plant  as  did  the  two  cotyledons  of  the  bean.  Although  we 
find  a  little  starch  in  the  corn  cotyledon,  still  it  is  evident  from 
our  tests  that  the  endosperm  is  the  chief  source  of  food  supply. 
The  study  of  a  thin  section  of  the  corn  grain  under  the  compound 
microscope  shows  us  that  the  starch  grains  in  the  outer  part  of 
the  endosperm  are  large  and  regular  in  size.  Those  near  the  edge 
of  the  cotyledon  are  much  smaller  and  quite  irregular,  having  large 
holes  in  them.  We  know  that  the  germinating  grain  has  a  much 
sweeter  taste  than  that  which  is  not  growing.  This  is  noticed  in 
sprouting  barley  or  malt.  We  shall  later  prove  that,  in  order  to 
make  use  of  starchy  food,  a  plant  or  animal  must  in 
some  manner  change  it  over  to  sugar.  That  starch 
is  being  changed  to  grape  sugar  in  the  germinating 
corn  grain  can  easily  be  shown  by  the  following 
experiment :  — 

Cut  lengthwise  through  the  embryo  half  a  dozen  grains  A  grain  of  corn, 

of  corn  that  have  just  begun  to  germinate.     Place  them  in  wlL-  C  cot 

a  test  tube  with  a  little  Fehling's  solution  and  heat  almost  yiedon;'  ^V 

to  the  boihng  point.     On  examination,  the  corn  grains  will  endosperm  ; 

be  seen  to  give  a  slight  reaction  for  the  sugar  test,  especially  h,    hypoco- 

along  the  edge  of  the  cotyledon  and  between  it  and  the  tyl;  P,  plu- 

endosperm.  mule. 

Digestion.  —  This  change  of  starch  to  grape  sugar  is  a  process 
of  digestion.  It  is  performed  by  means  of  a  substance  found  in 
the  cotyledon  known  as  a  digestive  ferment  or  enzyme.  The  enzyme 
found  in  the  cotyledon  of  the  corn,  which  changes  starch  to  grape 
sugar,  is  called  diastase. 

Demonstration.  The  action  of  diastase  on  starch.  —  Diastase  can  be  sepa- 
rated from  the  cotyledon.     It  is  here  used  in  the  form  of  a  powder. 

To  1  c.c.  of  starch  in  100  c.c.  of  water,  add  a  very  little  (1  gram)  of  dias- 
tase. Place  the  vessel  containing  the  mixture  in  a  warm  place,  \yhere  the 
temperature  will  remain  nearly  constant  at  about  98°  Fahrenheit.  Test 
part  of  the  contents  at  the  end  of  half  an  hour,  and  the  remainder  the  next 
morning,  for  starch  and  grape  sugar.  The  starch  in  the  latter  test  will  be 
found  to  be  completely  changed  to  grape  sugar. 

Experiment.  —  Select  nine  germinating  grains  of  corn;  remove  the  en- 
dosperm from  six  of  them.  Replace  the  endosperm  in  three  of  the  grains 
by  a  little  corn-starch  paste.  Place  all  nine  grains  on  netting  over  a  cup  of 
water,  so  that  the  roots  reach  the  water.  Keep  them  moist.  Watch  from 
day  to  day  to  see  which  seedlings  do  the  best.     Explain  the  experiment- 


74 


BOTANY 


The  use  of  the  endosperm  to  the  corn;  A,  seedhngs 
without  endosperm;  B,  seedlings  with  starch  in 
place  of  endosperm;  normal  seedlings  at  the 
center. 


Make  drawings  at  the  end  of 
two  weeks  to  explain  your  re- 
sults. Of  what  use  is  the 
endosperm?  Can  the  seed- 
ling make  use  of  the  food 
supply  given  it  in  the  corn- 
starch paste  ? 

Other  Foods  in  Corn 
Grain.  —  Other  foods  be- 
sides starch  and  sugar  are 
present  in  the  corn  grain. 
A  test  for  proteid  shows 
that  a  considerable 
amount  of  this  food  is  pres- 
ent. Oil  also  is  found.  In 
the  sweet  corn  that  we  eat 
water  forms  a  very  large 
percentage  of  its  composi- 
tion by  weight.  This  is 
true  of  most  plant  and  animal  foods  that  are  eaten  in  a  fresh  state. 

Fate  of  the  Parts  of  the  Em- 
bryo of  the  Bean,  the  Pea,  and 
the  Corn.  —  If  the  above  experi- 
ments with  reference  to  the  ger- 
mination of  peas,  beans,  and  corn 
have  been  carefully  obser^^ed,  you 
have  by  this  time  reached  veiy 
definite  conclusions  regarding  the 
use  of  each  part  of  the  seed  (or 
grain)  to  the  young  plant.  In 
all  specimens  the  hypocotyl  is 
found  to  give  rise  to  the  root 
system  of  the  young  plant  (and 
in  the  bean  to  part  of  the  stem), 
while  the  part  we  call  epicotyl 
forms  the  leafy  shoot.  The  func- 
tion of  the  cotyledons  differed  in 
all  specimens.     In  the  bean  they 

were    carried     up  above    ground;  The  germination  of  a  grain  of  corn. 


Seeds  And  seedlings 


75 


at  first  they  seemed  to  serve  as  leaves,  later  becoming  absorbed 
as  food  by  the  growing  seed.  In  the  pea  the  cotyledons  serve  as 
food,  but  remain  under  ground.  In  the  corn  the  single  cotyledon 
serves  as  an  organ  for  digesting  and  absorbing  food  from  the 
storehouse  of  food  known  as  the  endosperm. 

Monocotyledons  and  Dicotyledons.  —  Plants  that  bear  seeds 
having  but  a  single  cotyledon  are  called  monocotyledons.  The  corn 
is  an  example  of  such  a  plant.  Although  we  find  a  good  many 
monocotyledonous  plants  in  this  part  of  the  world,  this  group  is 
characteristic  of  the  tropics,  just  as  the  dicotyledons  are  the  type 
for  the  temperate  climate.  Sugar  cane  and  many  of  the  large 
trees,  such  as  the  date  palm,  palmetto,  and  banana,  are  examples. 
Among  the  common  monocotyledons  of  the  north  temperate  zone 
are  corn,  lily,  hothouse  smilax,  and  asparagus. 

Polycotyledons.  —  A  third  type  of  plant,  grouped  according  to 
the  number  of  cotyledons,  is  the  group  represented  by  the  pines 
and  their  kin. 

Pine  seedlings  may  be  grown  in  damp  moss  or  sawdust.  They  must  be 
started  at  least  three  weeks  before  they  are  needed  for  use  in  the  laboratory.^ 

The  Pine  Cone  and  its  Seeds.  —  Ma- 
terial should  be  gathered  in  the  fall 
and  early  summer.  Get  some  very 
young  cones  and  some  of  older 
growth  that  contain  seeds.  The 
pine  tree  bears  inconspicuous  flowers 
of  two  kinds,  pollen-bearing  and 
seed-forming.  Pollination  is  accom- 
plished by  the  wind,  the  cones  grow- 
ing as  the  result  of  fertilization. 
Notice  the  position  of  the  cone  on 
the  branch.  Compare  a  young  cone 
with  an  old  one.  You  will  find  in 
the  young  cones  that  the  scales  are 
green  in  color  and  are  cemented  to- 
gether by  the  sticky  resin  or  pitch. 
In  the  older  cones  the  seeds  are 
ready  for  dispersal.  They  usually 
take  two  summers  to  grow  to  ma- 
turity. Pull  back  one  of  the  scales 
making  up  the  cone  and  see  what 
happens.  How  is  the  seed  adapted  to 
be  scattered?    Draw  one  of  the  scales  ^  ,     ,       •      i 

of  the  cone  and  a  winged  seed  to  show  the  position  of  the  seed  when  in  place. 

If  you  cut  open  a  seed  lengthwise,  after  having  split  the  hard  outer  coat, 
you  wiU  find  the  tiny  embryo  in  the  center  of  the  seed,  surrounded  by  its 

1  See  Hunter  and  Valentine,  Manual,  page  75. 


Spruce  cone  and  scale  containing  winged 
seed.    Photographed  by  Overton. 


76 


BOTANY 


endosperm.  If  the  student  is  a  vefy  careful  observer, 
he  may  be  able  to  make  out  the  number  of  cotyledons 
in  the  young  plant.  There  are  fifteen  seed  leaves  in 
one  common  species  of  pine.  The  number  and  position 
are  better  seen  in  a  young  seedling  of  three  or  four 
weeks'  growth. 

The  Uses  of  Seeds.  —  Some  of  the  uses  of 
seeds  to  man  have  already  been  noted.  A  seed 
is  a  very  young  plant  usually  provided  with  a 
store  of  food  to  give  it  a  start  in  life.  Its  use  to 
the  parent  plant  is  incalculable,  for  it  is  by 
means  of  the  seed  that  a  plant  reproduces  its 
kind.  This  can  be  done,  as  we  shall  see  later, 
to  a  limited  degree  by  cuttings,  grafting,  and  in 
other  ways,  but  the  usual  way  is  by  the  produc- 
tion and  planting  of  seeds.  Not  only  does  a 
seed  serve  to  continue  a  species  of  plant  in  a  cer- 
tain locality^  but  it  serves  to  give  the  plant  a 
Pine  seedling.  foothold  in  uew  places.     Seeds  may  be  blown 

by  the  wind  or  carried  by  animals,  or  by  a  hundred  devices  work 
their  way  to  pastures  new,  there  to  establish  outposts  of  their 
kind. 

Immense  numbers  of  seeds  may  be  produced  by  a  single  plant. 
This  may  be  of  great  economic  importance.  A  single  pea  plant 
may  produce  twenty  pods,  each  containing  from  six  to  eight 
seeds.  This  would  mean  the  possibility  of  nearly  twenty-five 
thousand  plants  produced  from  the  original  parent  by  the  end  of 
the  second  season.  A  plant  of  Indian  corn  may  produce  over 
fifteen  hundred  grains  of  corn.  On  the  other  hand,  many  weeds 
produce  seed  in  still  greater  numbers.  A  single  milkweed  may 
set  free  over  two  thousand  seeds.  A  single  capsule  of  Jimson 
weed  has  been  found  to  hold  over  six  hundred  seeds.  The  thistle 
is  even  more  prolific. 

Some  seeds,  especially  those  of  weeds,  are  able  to  withstand 
great  extremes  of  heat  and  cold  and  still  to  retain  their  ability  to 
germinate.  Some  have  been  known  to  retain  their  vitality  for 
over  fifty  years.  In  plants,  the  seeds  of  which  show  unusual 
hardiness,  it  is  found  that  the  food  supply  is  often  so  placed  as 


SEEDS  AND  SEEDLINGS 


77 


to  protect  the  delicate  parts  of  the  embryo  from  injury.  The  food 
is  in  a  form  not  easily  dissolved  by  water  or  broken  up  by  the 
action  of  frost,  so  that  it  is  kept  in  a  hard  state  until  such  a  time 
as  it  can  be  softened  by  the  process  of  digestion  during  the 
growth  of  the  plant.  It  can  be  seen  that  plants  bearing  seeds 
having  some  of  the  above  characters  have  a  great  advantage  over 
plants  bearing  seeds  that  are  poorly  protected. 


Milkweed  fruit,  showing  method  of  seed  dispersal. 

External  Factors  which  determine  the  Growth  of  Seeds.^  —  We 
have  spent  some  time  in  the  consideration  of  seeds  simply  to  learn 
a  little  about  their  structure.  This  has  been  done  so  that  we 
may  understand  the  work  as  we  take  up,  by  means  of  the 
following  experiments,  some  of  the  factors  which  call  the  dormant 
seed  to  life.  We  know  that  a  dry  seed,  after  lying  dormant  and 
apparently  dead  for  months  and  sometimes  for  years,  will,  when 

^  In  making  experiments  it  is  important  to  exclude,  if  possible,  all  other  factors 
but  the  one  you  wish  to  determine. 


78 


BOTANY 


the  proper  stimuli  are  applied  to  it,  start  in  its  growth  into  a 
new  plant.     Let  us  see  what  these  stimuli  are. 

Effect  of  Water  on  Dry  Seeds.  —  Weigh  ten  dry  navy  beans;  leave  them  in 
water  over  night;  reweigh.  How  much  have  they  increased  in  weight? 
We  have  already  found  that  water  gets  into  the  seed  through  the  micropyle. 
It  can  be  proved  that  it  gets  in  through  the  seed  coat  as  well.  If  you  cover 
five  seeds  entirely  with  paraffin,  and  in  five  others  cover  the  hilum,  micropyle, 
and  half  of  the  remainder  of  the  coat,  a  difference  in  weight  and  size  will 
be  apparent  the  next  morning. 

Expansive  Force  of  Germinating  Seeds.  —  The  expansive  force  of  germinat- 
ing seeds  is  considerable.  You  have  noticed  that  the  bean  is  considerably 
larger  after  soaking. 

Fill  a  small  bottle  almost  full  of  dry  seeds  (beans  or  peas) ,  then  fill  the 
space  left  with  water;  wire  in  the  cork  tightly.     Leave  the  bottle  overnight 

and  note  the  results  next  morn- 
ing. Would  this  force  be  of  use 
in  getting  a  start  under  the  soil  ? 
Have  you  noticed  that  the  soil  is 
lifted  in  the  garden  by  the  rows 
of  germinating  peas  and  beans  just 
before  they  come  up  ?  Is  this  due 
entirely  to  the  expansive  force  of 
seeds  ?  Watch  future  experiments 
before  you  attempt  a  definite  an- 
swer. 

Will  a  Dry  Seed  germinate? — 
Place  a  layer  of  moist  blotting 
paper  or  sawdust  in  bottom  of 
each  of  three  cups  or  three  tin 
cans.  Soak  fifteen  navy  beans 
overnight.  Place  five  in  each 
dish.  Water  one  dish  so  as  to 
cover  the  seeds ;  water  the  second 
so  as  to  keep  sawdust  rather 
moist;  let  the  third  remain  unwatered.  Cover  the  cups  with  loose-fitting 
covers.  Make  daily  observations  of  the  number  germinating,  and  the  con- 
dition of  each  for  at  least  ten  days.  Put  the  results  in  tabular  form.  What 
amount  of  water  is  most  favorable  for  germination  of  the  navy  bean  ?  * 

Water  a  Factor  in  Germination.  —  A  dry  seed  will  not  germinate. 
Water  is  absolutely  necessary  to  start  the  forces  at  work  toward  growth. 
But  it  is  sometimes  difficult  to  determine  the  amount  of  water 
that  is  most  favorable  to  germination.  Some  seeds  require  a  great 
deal  of  water,  others  require  very  little. 

Will  a  Seed  grow  without  Air?  —  We  have  already  seen  that  in 
the  germinating  corn  plant  the  starch  stored  in  the  endosperm 
was  changed  to  grape  sugar  by  the  action  of  a  digestive  ferment 
called  diastase.     This  sugar  was  then  used  by  the  plant  as  food. 

*  See  Huiiter  and  Valentine,  Manual,  page  222. 


The  expansive  force  of  germinating  seeds.  The 
flower  pot  to  the  left  was  filled  with  dry 
beans,  a  block  of  wood  wired  on,  and  the 
whole  apparatus  placed  in  a  pail  of  water 
over  night.  The  right-hand  figure  shows 
the  result. 


SEEDS  AND  SEEDLINGS 


79 


In  other  words,  the  food  furnished  new  material  for  the  plant,  and 

energy  for  it  to  push  its  way  through  the  sawdust  or  soil.     We  have 

proved  that  energy  is  invariably  released  as  a  result  of  oxidation. 

It  will  be  of  interest,  then,  to  see 

if  the  grain  of  corn  or  other  seeds 

can   grow    without    a    supply    of 

oxygen. 

A  simple  method  is  as  follows,  al- 
though this  is  not  an  accurate  experi- 
ment: Place  25  to  50  soaked  beans  or 
peas  in  each  of  two  wide-mouth  bottles, 
6  oz.  to  12  oz.  Cork  and  seal  one;  leave 
the  other  uncorked,  taking  care  to  keep 
the  seeds  as  moist  as  in  the  covered 
jar.  Notice  any  differences  in  the  seeds 
for  at  least  one  week.  Make  drawings 
showing  your  results.* 


Experiment  to  show  the  effect  of  lack 
of  air  on  germination. 


A  more  accurate  method  of  determin- 
ing this  is  to  exclude  air  entirely  from  a 
gl^-ss  jar  or  bottle  in  which  germinat- 
ing seeds  had  previously  been  placed. 

Air  may  be  exhausted  by  means  of  an  air  pump.  If  the  tube  is  now  sealed 
by  heating  under  the  flame  of  a  burner,  the  seeds  will  be  left  in  an  air-tight 
jar,  A  jar  with  seeds  in  same  condition,  except  for  lack  of  air,  should  be 
kept  as  a  control  experiment. 

Why  did  not  the  seeds  in  the  covered  jar  germinate?  We 
have  seen  that  to  release  the  energy  contained  in  a  piece  of  coal 
we  must  burn  or  oxidize  it.  To  do  this  we  must  have  a  constant 
supply  of  fresh  air  containing  oxygen.  The  seed,  in  order  to  re- 
lease the  energy  contained  in  its  food  supply,  must  have  oxygen, 
so  that  the  oxidation  of  the  food  may  take  place.  Hence  a  con- 
stant supply  of  fresh  air  is  an  important  factor  in  germination.  It 
is  important  that  air  should  penetrate  between  the  grains  of 
soil  around  a  seed.  The  frequent  stirring  of  the  soil  enables  the 
air  to  reach  the  seed.  Air  also  breaks  down  some  materials  in 
the  soil  and  puts  them  in  a  form  that  the  germinating  seed  can 
use.  What  is  at  least  one  reason  why  the  farmer  plows  and  har- 
rows a  field  ?  What  is  at  least  one  important  use  of  the  earth- 
worm? 

*  See  Hianter  and  Valentine.  Manual.  nasrA  224. 


80  BOTANY 

Oxidation  in  the  Human  Body.  —  Exhale  strongly  through  a  straw  or  a 
glass  tube  into  limewater.  The  limewater  turns  milky,  showing  that 
oxidation  of  organic  matter  has  taken  place  within  the  body. 

If  now  a  glass  cylinder  in  which  has  been  placed  some  moist  blotting 
paper  on  which  a  handful  of  soaked  peas  or  beans  are  resting  is  left  over- 
night in  a  moderately  warm  room,  and  if  the  air  within  the  jar  is  tested 
the  following  morning,  carbon  dioxide  will  be  found  present.  How  shall 
we  explain  its  presence,  in  view  of  the  above  test  with  the  human  breath  ? 

Experiment.  —  Place  sawdust  in  each  of  two  small  boxes  (cigar  boxes  will 
do)  and  plant  an  equal  number  of  bean,  pea,  and  squash  seeds  in  each. 
Place  one  box  in  a  warm  room  (in  the  winter  near  a  radiator  or  stove), 
the  other  in  a  room  where  the  temperature  will  not  exceed  70°  Fahrenheit. 
Be  careful  to  give  each  box  the  same  conditions  of  light  and  moisture.  In 
which  box  do  seeds  first  germinate  ?  Which  box  shows  the  better  growth 
after  three  weeks  have  elapsed  ? 

Moderate  Temperature  Best. — Another  factor  influencing  the 
germination  of  seeds  is  that  of  temperature.  What  is  the  most 
favorable  temperature  for  the  germination  of  the  bean,  pea,  and 
squash  f  ^  From  this  experiment  we  find  that  although  a  high 
temperature  may  stimulate  the  seed  to  immediate  activity,  never- 
theless, later,  the  seeds  in  moderate  temperature  do  better  than 
those  in  the  heat.  The  temperature  at  which  different  seeds  ger- 
minate varies  greatly.  Those  of  you  who  have  a  garden  at  home 
know  that  even  some  varieties  of  seeds  germinate  at  lower  temper- 
atures than  others  of  the  same  species;  for  example,  early  peas, 
lettuce,  or  radish  seed.  As  a  general  rule,  increase  in  tempera- 
ture is  favorable  up  to  a  certain  point,  beyond  which  it  is  injuri- 
ous to  the  young  plant.  Can  you  determine  this  danger  point 
from  your  experiments  ? 

Light  has  a  certain  marked  effect  on  young  seedlings,  which 
will  be  considered  when  we  take  up  the  growth  of  the  stem  in 
more  detail. 

Selective  Planting.  —  Although  it  has  been  noticed  for  a  long  time  that 
healthy  seed  usually  produced  healthy  plants,  it  is  only  within  recent  years 
that  farmers  have  begun  to  appreciate  what  can  be  done  by  selective  plant- 
ing. By  selective  planting  we  mean  choosing  the  best  plants  and  planting  the 
seed  from  these  plants  with  a  view  of  increasing  the  yield.  In  doing  this  we  must 
not  necessarily  select  the  most  perfect  fruits  or  grains,  but  must  select  seeds 
from  the  best  plants.  A  wheat  plant  should  be  selected  not  from  its  yield 
alone,  but  from  its  ability  to  stand  disease  and  unfavorable  conditions. 
In  1862  a  Mr.  Fultz,  of  Pennsylvania,  found  three  heads  of  beardless  or  bald 

^  See  Hunter  and  Valentine,  Manual,  page  223. 


SEEDS  AND  SEEDLINGS 


81 


wheat  while  passing  through  a  large  field  of  bearded  wheat.  He  piclted 
them  out,  sowed  them  by  themselves,  and  produced  a  quantity  of  wheat  now 
known  as  the  Fultz  wheat  (known  favorably  all  over  the  world).  By  care- 
ful seed  selection,  some  western  farmers  have  increased  their  wheat  produc- 
tion by  25  per  cent.  This,  if  kept  up  all  over  the  United  States,  would  mean 
over  $100,000,000  a  year 
in  the  pockets  of  the  farm- 
ers 

Boys  and  girls  who  have 
gardens  of  their  own  can 
easily  try  experiments  in 
selection  with  almost  any 
garden  vegetables.  Corn 
is  one  of  the  best  plants  to 
experiment  with.  Gather 
for  planting  only  the  full- 
est ears  and  those  with  the 
largest  kernels.  You  must 
also  select  from  the  plants 
those  that  produce  the 
most  ears.  Plant  such 
corn  grains,  carefully  se- 
lected, in  a  plot  by  themselves  in  the  garden,  and  compare  their  yield  with 
that  of  the  non-selected  corn.  The  accompanying  picture  shows  what  can 
be  done  by  selection.  We  find  that,  by  what  is  known  as  a  law  of  heredity, 
like  produces  like;  hence  the  grow^th  in  the  case  of  the  selected  grains. 
Not  only  does  the  corn  produce  ears  with  a  greater  number  of  grains,  but 
it  may  improve  upon  the  quality  of  the  yield. 


a 


Improvement  of  com  by  selection;  a,  original  type; 
h,  improved  type  developed  from  it. 


Reference  Books 

for  the  pupil 

Andrews,  Botany  All  the  Year  Round,  pages  103-119.     American  Book  Company. 
Dana,  Plants  and  Their  Children,  pages  50-98.     American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life.     Chaps.  I,  II,  III,  XXV.     Gmn  and  Com- 
pany. 
Cornell  Nature  Study  Leaflets.  XXVIII,  XLII,  XLIV.     N.Y.  Dept.  of  Agriculture. 

FOR   THE   TEACHER 

Goodale,  Physiological  Botany.     American  Book  Company. 

Gray,  Structural  Botany.     American  Book  Company. 

Leavitt,  Outlines  of  Botany,  pages  7-23.     American  Book  Company. 

De  CandoUe,  Origin  of  Cultivated  Plants.     D.  Appleton  and  Company. 

MacDougal,  Plant  Physiology.     Longmans,  Green,  and  Company. 

Year  Book,  U.S.  Dept.  of  Agriculture,  1894,  1895,  1896,  1897,  1898,  1899,  1901. 

hunter's  BIOL.  —  6 


VII.     ROOTS   AND   THEIR  WORK 


The  development  of  a  bean  seedling  has  shown  us  that  the  root 
invariably  grows  first.    One  of  the  most  important  functions  of  the  root 

to  a  young  plant  is  that  of  a  holdfast,  an  anchor  to 
fasten  it  in  the  place  where  it  is  to  develop.  This 
chapter  will  show  us  very  many  other  uses  of 
the  root  to  the  plant,  the  taking  in  of  water, 
the  storage  of  food,  climbing,  etc.  All  other 
functions  than  the  first  one  stated  arise  after 
the  young  plant  has  begun  to  develop. 

Root  System}  —  If  you  dig  up  a  young  bean  seed- 
ling and  carefully  wash  off  the  roots,  you  will  see  that 
a  long  root  is  developed  as  a  continuation  of  the  hypo- 
cotyl.  This  root  is  called  the  primary  root.  Other 
smaller  roots  which  grow  from  the  primary  root  are 
called  secondary,  or  tertiary,  depending  on  their  relation 
to  the  first  root  developed.  In  a  young  plant,  notice 
the  general  direction  taken  by  the  roots.  Can  you  give 
any  reason  for  the  spreading  out  of  the  roots  in  all 
directions  ? 

Make  a  drawing  of  the  root  system  of  a  seedling; 
label  all  its  parts. 


Young  bean  plant, 
showing  primary 
and  secondary 
roots. 


Downward  Growth  of  Root.  —  Most  of  the  roots  examined  take 
a  more  or  less  downward  direction.  We  have  already  seen  that 
factors  outside  of  the  seed  call  it  into  activity  and  cause  what  we 
call  germination.  Might  external  factors  cause  the  root  to  grow 
downward,  and  if  so,  what  are  the  factors? 

The  following  apparatus  and  experiments  will  throw  some  light 
on  this  question. 

The  Pocket  Garden}  —  A  very  convenient  form  of  pocket  germinator 
may  be  made  in  a  few  minutes  in  the  following  manner:  Obtain  two 
cleaned  four  by  five  negatives  (window  glass  will  do) ;  place  one  fiat  on  the 
table  and  place  on  the  glass  half  a  dozen  pieces  of  colored  blotting  paper 
cut  to  a  size  a  little  less  than  the  glass.  Now  cut  four  thin  strips  of  wood  so 
as  to  fit  on  the  glass  just  outside  of  the  paper.     Next  moisten  the  blotter, 


*  See  Hunter  and  Valentine,  Mantud,  page  20. 

82 


2  Ibid.,  page  233. 


ROOTS   AND   THEIR  WORK 


83 


A  pocket  germinator,  in  which  the  roots  of  the  barley 
seedlings  show  a  turning  in  response  to  gravity.  The 
germinator  was  originally  turned  180°  from  its  present 
position. 


place  on  it  some  well- 
soaked  radish  or  mustard 
seeds  or  grains  of  barley, 
and  cover  it  with  the 
other  glass.  The  whole 
box  thus  made  should  be 
bound  together  with  bi- 
cycle tape.  Seeds  will 
germinate  in  this  box,  and 
with  care  may  live  for 
two  weeks  or  more. 

Influence  of  Gravity. 
—  We  are  all  familiar 
with  the  fact  that  the 
force  we  call  gravity 
influences  life  upon  this  earth  to  a  great  degree.  Might  gravity 
act  on  the  growing  root  ?  This  question  may  be  answered  by  the 
following  simple  experiment: 

Place  your  pocket  garden  on  one  edge  and  allow  the  seeds  to  germinate 
until  the  root  has  grown  to  a  length  of  about  half  an  inch.  Then  turn  the 
box  at  right  angles  to  the  first  position.     Allow  it  to  remain  for  one  day 

^_,  undisturbed,  and  then  examine  it.  The  roots 
will  be  found  to  have  turned  in  response  to 
the  change  in  position.  In  what  part  of  the 
root  does  the  change  take  place?  What 
part  of  the  growing  root  is  most  easily  in- 
fluenced by  the  force  of  gravity?  Make  a 
series  of  drawings  to  illustrate  this  experi- 
ment. This  experiment  seems  to  indicate  that 
the  roots  are  influenced  to  grow  downward  by 
the  force  we  call  gravity. 

Experiments  to  determine  Influence 
of  Moisture    on    a   Growing    Root.  — 

The  objection  might  well  be  interposed 
that  the  roots  in  the  pocket  garden 
grew  downward  after  water.  This  is 
unlikely,  however,  as  the  air  in  the 
germinator  is  saturated  with  moisture. 
That  moisture  has  an  influence  on  the 
growing  root  is  easily  proved. 


Revolve  this  figure  in  the  direc- 
tion of  the  arrows  to  see  if  the 
roots  of  the  radish  respond  to 
gravity. 


Plant  bird  seed  or  the  seed  of  mustard  or  radish  in  the  under  side  of  a 
sponge,  which  should  be  kept  wet,  and  may  be  suspended  by  a  string  under 
a  bell  jar  in  the  schoolroom  window.  Note  whether  the  roots  leave  the 
sponge  to  grow  downward,  or  if  the  moisture  in  the  sponge  is  suflBcient  to 
counterbalance  the  force  of  gravity. 


84 


BOTANY 


Another  experiment  is  the  following:  Divide  the  interior  of  a  shallow 
wooden  box  into  two  parts  by  an  incomplete  partition.  Partly  fill  the  box 
with  sawdust  and  place  the  opening  in  the  partition  so  that  it  is  below  the 
surface  of  the  sawdust.  Plant  peas  and  beans  in  the  sawdust  on  one  side  of 
the  partition,  water  very  slightly,  but  keep  the  other  side  of  the  box  well 
soaked.  After  two  weeks,  take  up  some  of  the  seedlings  and  note  the  efifect 
on  the  roots. 

Water  a  Factor  which  determines  the  Course  taken  by  Roots. — 

Water,  as  i^ell  as  the  force  of  gravity,  has  much  to  do  with  the  direction 

taken  by  roots.  The  smaller 
roots,  especially,  are  influ- 
enced by  moisture.  Mois- 
ture also  determines  the  kind 
and  abundance  of  roots  on 
a  plant.  Water  is  always 
found  below  the  surface 
of  the  ground,  but  some- 
times at  a  great  depth. 
In  order  to  obtain  a  sup- 
ply of  water,  the  roots  of 
plants  frequently  spread 
out  for  very  great  dis- 
tances. Most  trees,  and 
all  grasses,  have  a  greater 
area  of  surface  exposed 
by  the  roots  than  by  the 
branches.  The  mesquite 
bush,  a  low-growing  tree 
of  the  American  and  Mexi- 
can deserts,  often  sends 
roots  downwards  for  a  distance  of  forty  feet  after  water.  The 
dandelion  shown  in  the  cut  has  a  greater  depth  below  the  surface 
of  the  ground  than  appears  above  the  surface.  The  roots  of 
alfalfa,  a  common  plant  used  for  hay  in  the  Western  states, 
often  penetrate  the  soil  to  a  distance  of  ten  to  twenty  feet  below 
the  surface  of  the  ground. 

The  force  of  gravity  is  an  exciting  cause  or  stimulus  to  the 
growth  of  plants.  The  reaction  of  the  plant  (or  any  living  thing) 
to   this    force   is   called    geotropism.      Roots    are   stimulated    by 


Dandelion  plant.     Photographed  by  Overton. 


ROOTS  AND  THEIR  WORK 


85 


gravity  to  grow  downward ;  hence  they  are  said  to  be  positively 
geotropic. 

The  force  with  which  roots  grow  downward  is  greater  than  the  down- 
ward pull  exerted  by  gravity  on  the  growing  root. 

Windsor  Bean  Experiment.  —  Place  a  grow- 
ing Windsor  bean  so  that  the  plant  is  held  by 
a  pin  through  the  cotyledons  and  the  root 
directed  downward  into  a  dish  of  mercury. 
The  root  will  push  its  way  into  this  very  dense 
substance. 

Or  a  germinating  bean  may  be  so  fastened 
that  the  root  will  point  downward  into  a  groove 
made  in  a  little  wooden  or  cork  float  which  is 
placed  on  the  surface  of  a  dish  of  water  directly 
under  the  bean.  If  the  experiment  is  success- 
ful, the  root  will  push  the  float  either  under 
water  or  out  of  the  way.^ 


Effect  of  Gravity  on  the  Stem. —  The 

stem,  on  the  other  hand,  seems  to  be 
affected  in  the  opposite  manner,  and  is 
therefore  said  to  be  negatively  geotropic. 


Experiment  to  show  the  effect 
of  gravity  upon  the  growth 
of  stem  and  root.  (After 
McDougall.) 


Figure  to  show  the  point 
of  most  rapid  growth 
in  the  root  of  the 
bean.  (After  McDou- 
gall.) 


The  effect  of  gravity  on  the  young  stem  may  be 
shown  by  turning  upside  down  a  pocket  garden  in 
which  are  young  barley  or  corn  plants.  The  stt  m 
at  once  turns  upward  again.  The  same  thing  may 
be  proved  by  germinating  radish  or  grass  setds  on 
the  under  side  of  a  hanging  sponge.  After  the  st(  m 
has  attained  a  length  of  one  or  two  inches,  turn 
the  sponge  so  that  the  young  plants  are  upside 
down. 

Place  where  Root  grows  Most  Rapidly.  —  Select 
three  or  four  pea  seedlings  which  have  roots  half  an 
inch  to  an  inch  in  length.  Mark  such  roots  on  their 
outer  surface  at  equal  intervals  (say  one  mm. 
apart)  by  means  of  a  thread  dipped  in  India  ink. 
Allow  these  marks  to  be  continued  on  strips  of 
paper  which  are  placed  next  to  the  growing  roots. 
Keep  them  in  a  moist  germinator  for  several  days 
Make  drawings  to  show  where  increase  in  length 
took  place. 


The  Root  Cap  and  Most  Rapid  Point  of 
Growth.  —  If  we  examine  a  longitudinal  section  of 
any  dicotyledonous  root  under  the  microscope  we 
find  that  at  the  very  tip  of  the  root  can  be  seen  a  collection  of  cells  arranged 
more  or  less  loosely  over  the  end  of  the  root  in  the  form  of  a  cap.  Most  of 
these  cells  are  dead,  and  this  root  cap  is  simply  an  adaptation  to  protect  the 

^  See  Hunter  and  Valentine,  Manual,  page  232. 


86 


BOTANY 


tender  growing  point  of  the  root.     Just  beneath  the  root  cap  is  a  collection 
of  tiny,  thin-walled  cells.     At  that  point  the  cells  are  engaged  in  dividing 

into  new  cells  very  rapidly  indeed.  This 
is  the  point  of  most  rapid  growth  in  the 
root. 


How  the  Root  takes  in  Water.  —  That 
the  root  of  a  plant  is  attracted  by  water 
and  is  also  stimulated  by  gravity  has 
been  already  shown.  Let  us  now  attempt 
to  solve  the  question  of  how  the  root 
takes  in  water.  To  help  us  in  obtaining 
our  answer  we  should  examine  the  pocket 
gardens  which  we  planted  a  few  days  previously.  Look  carefully  at  the 
tiny  roots  of  barley  or  corn,  and  you  will  find  that  they  are  covered  in  places 
with  what  looks  like  a  fuzzy  growth.  These  hairlike  structures  are  called 
root  hairs.    What  is  the  color  of  the  root  hairs  to  the  naked  eye  ?     Where 


The  end  of  a  growing  root,  tipped  and 
protected  by  the  root  cap;  g,  the 
growing  point.  (Considerably  mag- 
nified.) 


Root  hairs  of  barley.    The  white  appearance  of  the  roots  is  due  to  these  organs  of 

absorption. 


are  the  root  hairs  largest  ?  Where  are  they  longest  ?  Where  are  they  most 
abundant?  Try  giving  your  pocket  garden  more  water;  what  is  the  effect 
on  the  root  hairs?  Can  you  get  a  similar  result  by  cutting  off  the  water 
supply  of  the  roots  ?  Do  root  hairs  ever  disappear  after  once  coming  out 
on  the  root  ? 

Structure  of  a  Taproot.  —  To  understand  fully  the  relation  of 
the  root  hairs  to  the  rest  of  the  root,  it  will  be  necessary  for  us  to 
examine  some  large,  fleshy  root  (a  taproot),  so  that  we  may  get 


ROOTS   AND   THEIR  WORK 


87 


A  cross  section  through  a  taproot  (a 
parsnip);  C,  cortex;  W,  wood.  Notice 
in  the  right-hand  specimen,  which 
has  been  dipped  in  iodine,  that  the 
core  of  wood  continues  out  into  the 
rootlets  which  leave  the  main  root. 
Where  is  most  starchy  food  stored  in 
a  parsnip  ? 


a  little  first-hand  evidence  as  to  its  internal  structure.  If  you 
cut  open  a  parsnip  or  carrot  so  as  to  make  a  cross  section  of  the 
root,  you  find  two  distinct  areas,  an  outer  portion,  the  cortex,  and 
an  inner  part,  the  central  cylinder. 
If  you  cut  another  parsnip  in 
lengthwise  section,  these  struc- 
tures show  still  more  plainly.  An 
additional  fact  is  seen;  namely, 
that  all  the  smaller  roots  leaving 
the  main  or  primary  root  have  a 
core  of  wood  which  bores  its  wav 
out  through  the  cortex  wherever 
the  small  rootlets  are  given  off. 
Make  a  drawing  that  will  show 
these  points. 

Fine  Structure   of  a  Root.  —  If 
we  could  now  examine  a  much  smaller 
and  more  delicate  root  in   thin   longi- 
tudinal section  under  the  compound  microscope,  we  should  find  the  follow- 
ing structure:    (Cross  sections  and  longitudinal  sections  of  Tradescantia 
roots  are  excellent  for  demonstration  of  these  structures.)     The  entire  root 
is  seen  to  be  made  up  of  cells,  the  walls  of  which  are  uniformly  rather  thin. 

The  cells  of  this  part  of  the  root  are 
more  or  less  regular  in  size  and  shape. 
The  central  cylinder  can  easily  be  dis- 
tinguished from  the  surrounding  cortex. 
The  cells  of  the  former  have  somewhat 
thicker  walls.  In  a  longitudinal  sec- 
tion a  series  of  tubelike  structures  may 
be  found  within  the  central  cylinder. 
These  structures  are,  in  fact,  cells  which 
have  grown  together  at  the  small  end, 
the  long  axis  of  the  cells  running  the 
length  of  the  main  root.  In  their  de- 
velopment the  cells  mentioned  have 
grown  together  in  such  a  manner  as  to 
lose  their  small  ends,  and  now  form 
continuous  hollow  tubes  with  rather 
strong  walls.  Other  cells  have  come  to 
develop  greatly  thickened  walls;  these  cells  give  mechanical  support  to  the 
tubelike  cells. 


Cross  section  of  a  young  taproot;  a,  a, 
root  hairs;  b,  epidermis;  c,  cortical 
layer;  d,  fibrovascular  cylinder. 


88 


BOTANY 


Young  embryo  of  corn, 
showing  root  hairs 
(R.H.)  and  growing 
stem  (-P.)' 


Fibrovascular  Bundles.  —  Collections   of   such  tubes  and  sup- 
porting woody  cells  together  make  up  what  is  known  as  fibro- 
vascular bundles. 

Structure  of  a  Root  Hair.  —  The  cells  of 
the  cortex  are  almost  uniform  in  character. 
The  outmost  layer,  however,  differs  from 
the  rest  of  the  cortex.  This  layer  is 
called  the  epidermis.  It  is  the  prolongations 
of  the  cells  of  the  epidermis  that  form  the 
structures  we  have  already  seen  and  know 
as  root  hairs. 

Let  us  now  take  out  one  of  the  small 
radish  seedlings  from  the  pocket  garden, 
mount  it  in  water,  and  examine  it  under 
the  low  power  of  the  microscope.  A  single 
root  hair  will  be  found  to  be  a  long  round 
structure,  almost  colorless  in  appearance. 
The  wall,  which  is  very  flexible  and  thin,  is 

made  up  of  cellulose,  a  substance  somewhat  like  wood  in  chemical 

composition,  through  which  fluids  may  easily  pass.     If  we  had  a 

very  high  power  of   the  microscope  focused  upon  this  cellulose 

wall,  we  should  be  able  to  find  under  it  another 

structure,  far  more  delicate  than  the  cell  wall. 

This  is  called   the   cell   membrane.      Clinging 

close  to  the  cell  membrane  is  the  protoplasm 

of  the  cell,  which   in   the   root   hair  is  found 

close  to  the  membrane.     The  interior  of  the 

root  hair  is  more   or  less   filled  with  a  fluid 

called  cell  sap.     Forming  a  part  of  the  living 

protoplasm  of  the  root  hair,  sometimes  in  the 

hairlike  prolongation  and   sometimes   in  that 

part  of  the  cell  which  forms  the  epidermis,  is 

found    a   nucleus.     The   protoplasm,  nucleus, 

and  cell  membrane  are  alive;   all  the  rest  of 

the  root  hair  is  dead  material,  formed  by  the 

activity   of   the  living  substance  of    the   cell. 

The  root  hair  is  a  living  plant  cell  with  a  wall 


Diagram  of  a  root 
hair:  CM.,  cell 
membrane;  C.S., 
cell  sap;  C.W.,  cell 
wall;  P,  proto- 
plasm; N,  nucleus; 
S,  soil  particles. 


ROOTS  AND  THEIR  WORK 


89 


so  delicate  that  water  and  mineral  substances  from  the  soil  can 
pass  through  it  into  the  interior  of  the  root. 

How  THE  Root  absorbs  Water.  —  This  process  can  best  be  under- 
stood by  means  of  the  following  experiment:  ^  Crack  the  shell  of  a  fresh  egg 
at  one  end  and  pick  it,  bit  by  bit,  from  the  delicate  membrane  that  lies 
underneath  it  until  about  one  square  inch  of  the 
membrane  is  exposed.  Now  break  a  small  hole  in  the 
opposite  end  of  the  egg  just  large  enough  to  admit  a 
small  glass  tube.  After  putting  the  tube  in  place, 
cement  it  in  with  sealing  wax  or  paraffin.  Place  the 
egg  with  the  large  end  in  a  glass  of  water.  Examine 
it  after  a  few  hours,  and  the  contents  of  the  egg  will  be 
found  to  have  risen  in  the  glass  tube  to  a  considerable 
distance.  The  membrane  through  which  the  water 
has  passed  has  no  holes  in  it.  It  allows  the  passage 
of  certain  fluids  through  it,  and  is  hence  called  a 
permeable  membrane.  In  the-  experiment  just  per- 
formed, a  little  of  the  contents  of  the  egg  passes  into 
the  glass,  as  can  be  proved  by  the  proteid  test  applied 
to  the  contents  of  the  glass.  On  the  other  hand,  a 
considerable  amount  of  water  from  the  glass  has 
passed  into  the  egg  through  the  membrane. 

Osmosis.  —  The  'process  hy  which  two  fluids, 
separated  by  a  membrane,  pass  through  the 
membrane  and  mingle  with  each  other  is  called  osmosis.  In  this 
process  the  greater  flow  is  always  toward  the  more  dense  medium. 
The  method  by  which-  the  root  hairs  take  up  soil  water  is  exactly 
the  same  process  as  we  see  in  the  egg.  It  is  by  osmosis.  The 
white  of  the  egg  is  the  best  possible  substitute  for  living  matter; 
it  has,  indeed,  almost  the  same  chemical  formula  as  protoplasm. 
The  animal  membrane  separating  the  egg  from  the  water  is  much 
like  the  delicate  membrane  which  separates  the  protoplasm  of 
the  root  hair  from  the  water  in  the  soil  surrounding  it.  The  fluid 
in  the  root  hair  is  more  dense  than  the  soil  water;  hence  the 
greater  flow  is  toward  the  interior  of  the  root  hair. 

Passage  of  Soil  Water  within  the  Root.  —  We  have  already  seen 
that  in  an  exchange  of  fluids  by  osmosis  the  greater  flow  is 
always  toward  the  denser  fluid.     Thus  it  is  that  the  root  hairs 

*  This  experiment,  although  not  illustrating  osmotic  action  in  the  strict  sense, 
appeals  to  the  pupil  as  does  no  other. 


Experiment  to  show 
osmosis  in  an  egg; 
L,  level  of  the  fluid 
in  the  tube. 


90 


BOTANY 


A  potato  osmometer.  The  lower  end  of  the  potato  was  cut  off  and  the  remainder  peeled  for 
about  one  third  of  its  length.  A  hole  was  bored  to  within  three  fourths  of  an  inch  of  the 
cut  end;  a  small  hole  was  bored  at  the  side  of  the  potato.  In  the  latter  was  inserted  a 
small  L-shaped  tube,  the  lower  end  being  vaselined  to  make  it  air  tight.  Sugar  was  then 
placed  in  the  hole  at  the  top  and  a  cork  inserted;  water  was  poured  into  the  dish  be- 
low.   Within  two  hours  the  water  had  risen  in  the  tube  as  shown  in  the  right-hand  figure. 

take  in  more  fluid  than  they  give  up.  The  cell  sap,  which  partly 
fills  the  interior  of  the  root  hair,  is  a  fluid  of  greater  density  than 
the  water  outside  in  the  soil.  When  the  root  hairs  become  filled 
with  water,  the  density  of  the  cell  sap  is  lessened,  and  the  cells  of 
the  epidermis  are  thus  in  a  position  to  pass  along  their  supply  of 
water  to  the  cells  next  to  them  and  nearer  to  the  center  of  the  root. 
These  cells,  in  turn,  become  less  dense  than  their  inside  neighbors, 
and  so  the  transfer  of  water  goes  on  until  the  water  at  last  reaches 
the  central  cylinder.  Here  (as  we  shall  see  later)  it  is  passed  over 
to  the  tubes  of  the  fibrovascular  bundles  and  started  up  the 
stem.  The  pressure  created  by  this  process  of  osmosis  is  suffi- 
cient to  send  water  up  the  stem  to  a  distance,  in  some  plants,  of 
twenty-five  to  thirty  feet.  Cases  are  on  record  of  water  having 
been  raised  in  the  birch  a  distance  of  eighty-five  feet.  How  water 
gets  to  the  summits  of  tall  trees  is  a  problem  which  we  shall  dis- 
cuss in  a  later  chapter. 

Physiological  Importance  of  Osmosis.  —  It  is  not  an  exaggera- 
tion to  say  that  osmosis  is  a  process  not  only  of  great  importance 


HOOTS  AND   THEIR  WORK 


91 


to  a  plant,  but  to  an  animal  as  well.  Foods  are  digested  in  the 
food  tube  of  an  animal;  that  is,  they  are  changed  into  a  soluble 
form  so  that  they  may  pass  through  the  walls  of  the  food  tube 
and  become  part  of  the  blood.  Without  the  process  of  osmosis 
we  should  be  unable  to  use  the  food  we  eat. 

Composition  of  Soil.  —  If  we  examine  a  mass  of  ordinary  loam 
carefully,  we  find  that  it  is  composed  of  a  number  of  particles  of 
varying  size  and  weight.  Between  these  particles,  if  the  soil  is 
not  caked  and  hard  packed,  we  can  find  tiny  spaces.  In  well- 
tilled  soil  these  spaces  are  constantly  being  formed  and  enlarged. 
They  allow  air  and  water  to  penetrate  the  soil.  If  we  examine 
soil  under  the  microscope,  we  find  considerable  water  clinging  to 
the  soil  particles  and  forming  a  delicate  film  around  each  particle. 
In  this  manner  most  of  the  water  is  held  by  the  soil. 


Experiment  to  illustrate  the  kind  of  soil  which  best  retains  water:  A,  gravel;  B,  sand; 
C,  barren  soil;  D,  rich  soil;  E,  leaf  mold;  F»  dry  leaves. 

Kind  of  Soil  Favorable  to  Evaporation.  —  The  picture  shows  an 
easily  constructed  apparatus  to  show  which  kind  of  soil  can  retain  most 
water.  Fill  each  of  the  vessels  with  a  given  weight  (say  100  grams 
each)  of  gravel,  sand,  barren  soil,  rich  loam,  leaf  mold,  and  25  grams 
of  dry  pulverized  leaves,  then  pour  equal  amounts  of  water  (100  c.c.)  on 
each.  Measure  all  that  runs  through.  The  water  that  has  been  retained 
constitutes  the  water  supply  that  plants  could  draw  on  from  such  soil. 

How  Water  is  held  in  Soil.  —  To  understand  what  comes  in  with  the 
soil  water,  it  will  be  necessary  to  find  out  a  httle  more  about  soil.  Scientists 
who  have  made  the  subject  of  the  composition  of  the  earth  a  study,  tell  us 


92 


BOTANY 


Inorganic  soil  is  being  formed  by  weathering. 


that  once  upon  a  time  at  least 
apart  of  the  earth  was  molten. 
Later,  it  cooled  into  solid  rock. 
Soil-making  began  when  the 
ice  and  frost,  working  with  the 
heat,  chipped  off  pieces  of  rock. 
These  pieces  in  time  became 
ground  into  fragments  by  action 
of  ice,  glaciers,  or  the  atmos- 
phere. This  process  is  called 
weathering.  Weathering  is 
largely  a  process  of  oxidation. 
A  glance  at  crumbling  stone 
will  convince  you  of  this,  be- 
cause of  the  oxide  of  iron  (rust)  disclosed.  So  by  slow  degrees  this  earth 
became  covered  with  a  coating  of  what  we  call  inorganic  soil.  Later,  gen- 
eration after  generation  of  tiny  plants  and  animals  which  lived  in  the 
soil  died,  and   their  remains  formed  the  first  organic  materials  of  the  soil. 

You  are  all  familiar 
with  the  difference  be- 
tween the  so-called  rich 
soil  and  poor  soil.  The 
dark  soil  simply  contains 
more  dead  plant  and 
animal  life,  which  forms 
the  portion  called  humus. 
A  simple  experiment 
may  be  performed  to 
show  the  amount  of  vege- 
table and  mineral  mat- 
ter in  different  soils. 

Amount  of  Organic 
Matter  in  Soil.  —  Gather 
about  a  pound  of  leaf 
mold  from  a  forest,  a  like 
amount  of  the  rich  loam 
taken  from  beneath  the 
leaf  mold,  and  the  same 
amount  of  soil  taken  from 
a  barren  roadside  or 
field.  Dry  them  carefully 
and  then  weigh  equal 
amounts  (say  100  grams) 
of  each  kind  of  soil. 
Place  them  on  pieces  of 

tin  and   heat   them    red-  This  picture  shows  how  the  forests  help  to  cover  the 

hot  over  a  coal  fire  or  in  inorganic  soil  with  an  organic  coating. 


ROOTS   AND   THEIR  WORK  93 

a  furnace  until  you  feel  sure  that  all  organic  matter  is  burned  up.  Then  re- 
weigh  each  and  put  the  soil  into  three  bottles,  giving  the  weight  before  and 
after  burning  in  each  case.  Professor  Hodge  (see  Nature  Study  and  Life, 
page  380)  tried  this  experiment,  and  found  that  when  each  lot  originally 
weighed  100  grams,  the  forest  leaf  mold  in  burning  lost  78  grams,  the  forest 
loam  lost  11  grams,  while  the  barren  soil  lost  only  1  gram.  What  results  do 
you  get  from  your  experiment? 

The  Root  Hairs  take  more  than  Water  out  of  the  Soil.  —  If  a 

root  containing  a  fringe  of  root  hairs  is  washed  off  carefully,  it 
will  be  found  to  have  little  particles  of  soil  still  clinging  to  it. 
Examined  under  the  microscope,  these  particles  of  soil  seem  to 
be  fastened  to  the  root  hair.  The  following  experiment  explains 
what  the  root  hairs  do  to  the  soil  surrounding  them. 

Grow  a  number  of  seedlings  in  a  tumbler  between  blotting  paper  and 
the  edge  of  the  glass  or  in  a  pocket  garden.  Place  a  sheet  of  blue  '  litmus 
paper  so  that  the  root  will  grow  against  it.  Does  a  change  of  color  take 
place  near  the  root  hairs? 

Acid  Reaction  of  Root  Hairs.  —  The  change  of  color  of  the 
litmus  paper  from  a  blue  to  red  shows  us  that  the  growing  root 
hairs  have  a  decidedly  acid  reaction.  Thus  some  mineral  matters 
which  otherwise  could  not  be  taken  into  the  root  hair  are  dis- 
solved by  the  action  of  the  acid.  Lime  (oxide  of  calcium),  for 
instance,  is  such  a  mineral.  The  minerals  that  the  root  hairs 
take  in  with  the  soil  water  are  calcium,  potassium,  iron,  silicon, 
and  other  elements,  in  very  small  quantities.  If  radish  or  other 
seedlings  be  grown  in  moist,  rich  soil,  and  then  removed  when 
but  an  inch  in  height,  the  soil  will  be  found  to  cling  to  the  root 
hairs.  In  fact,  the  surface  of  the  root  hair  often  almost  incloses 
tiny  particles  of  soil,  the  acid  given  out  literally  eating  away  the 
soil  particles  thus  inclosed. 

The  proportion  of  each  of  these  mineral  materials  is  very  small 
compared  with  the  water  in  which  they  are  found.  A  very  great 
amount  of  water  must  be  taken  up  by  the  roots  in  order  that 
the  plant  may  get  the  needed  amount  of  mineral  matter  with 
which  to  build  its  protoplasm.     We  also  find  that  some  mineral 

1  The  blue  litmus  paper  contains  a  vegetable  material  which  turns  red  in  the 
presence  of  an  acid.  Red  litmus  paper  changes  back  from  red  to  blue  when  an 
alkaline  medium  is  present,  ^^llen  a  substance  will  not  change  either  red  or  blue 
litmus  paper,  it  is  said  to  be  neutral. 


94 


BOTANY 


matters  are  taken  in  far  in  excess  of  the  immediate  needs  of  the 
plant.     Such  minerals  are  stored  in  the  stem  and  leaves. 

Need  of  Mineral  Matter  for  Growth.  —  Plants  will  not  grow  well 
without  certain  of  these  mineral  substances.  This  can  be  proved 
by  the  growth  of  seedlings  in  a  so-called  nutrient  solution.  Such  a 
solution  contains  all  the  mineral  matter  that  a  plant  uses  for  food.^ 

Mineral  Matter  necessary  for  Growth  of  Young  Plants.  —  Obtain  three 
jars ;  put  distilled  water  in  one,  nutrient  solution  (without  ferric  chloride) 
in  another,  and  nutrient  solution  plus  ferric  chloride  in  the  third.  Place 
germinating  corn  or  bean  seedlings  in  the  jars  so  that  roots  extend  down 
into  the  liquids.  Observe  the  growth  of  the  three  lots  of  seedhngs.  Decide 
which  of  the  three  jars  is  most  favorable  to  growth. 

Nitrogen  in  a  Usable  Form  necessary  for  Growth  of  Plants.  —  We 

learned  that  humus  is  made  up  of  decayed  plant  and  animal 
bodies.  A  chemical  element  needed  by  the  plant  to  make  proto- 
plasm is  nitrogen.     This  element  cannot  be  taken  from  either  soil 

water  or  air  in  a  pure  state,  as  is  the  case  with 
the  other  chemical  elements  used  by  the  plant 
in  the  manufacture  of  protoplasm.  Nitrogen  is 
usually  obtained  from  the  organic  matter  in  the 
soil,  where  it  exists  with  other  substances  in 
the  form  of  nitrates.  Nitrogen  is  found  in  such 
form  in  all  decaying  material ;  hence  the  use  of 
fertilizers.^ 

Relation  of  Bacteria  to  Nitrogen.  —  It  has 
been  known  for  a  long  time  that  clover,  peas, 
beans,  and  other  legumes,  cause  the  ground  to 
become  more  favorable  for  growth  of  other  plants.  The  reason 
for  this  has  been  discovered  in  late  3^ears.     On  the  roots  of  the 

^  A  nutrient  solution  may  be  prepared  as  follows :  — 

Distilled  water  (H2O) 1000.00    c.c. 

Potassium  nitrate  (KNO3) 1.00    gram 

Sodium  chloride  (NaCl) 0.50    gram 

Calcium  sulphate  (CaS04) 0.50    gram 

Magnesium  sulphate  (MgS04) 0.50    gram 

Calcium  phosphate  (Ca3[P04]2) 0.50    gram 

Ferric  chloride  (FeCls) 0.005    gram 

(Do  not  put  the  ferric  chloride  into  the  solution  in  the  first  place,  but  add  a  drop 
of  it  to  each  bottle  wlien  the  seedlings  are  put  in.) 

^  Other  important  plant  foods  found  in  soil,  but  which  are  frequently  used  up  by 
plants  growing  therein,  are  potash  and  phosphoric  acid.  Both  of  these  substances 
are  made  soluble  so  as  to  be  taken  in  by  the  root  by  the  action  of  the  carbon  dioxide 
in  the  soil. 


Bacteroids  forming 
from  filamentous 
structures  in  the 
cells  of  a  root. 


ROOTS  AND  THEIR  WORK 


95 


it  rate  5  x. 


plants  mentioned  are  found  little  swellings  or  tubercles;  in  the 
tubercles  exist  millions  of  tiny  plants  called  bacteria,  which 
take  out  nitrogen  from  the  at- 
mosphere and  fix  it  so  that  it 
can  be  used  by  the  plant ;  that 
is,  they  form  nitrates  for  the 
plants  to  use.  These  bacteria, 
alone  of  all  the  living  plants, 
have  the  power  to  take  the  free 
nitrogen  from  the  air  and  make 
it  over  into  a  form  that  can  be 
used  by  the  roots. 

This  fact  is  made  use  of  by 
careful  farmers  who  wish  to 
make  as  much  as  possible  from 
a  given  area  of  ground  in  a  given 
time.  Such  plants  as  are  hosts 
for  the  nitrogen-fixing  bacteria 
are  planted  early  in  the  season. 
Later  these  plants  are  plowed  in 
and  a  second  crop  is  planted. 
The  latter  grows  quickly  and  lux- 
uriantly because  of  the  nitrates 
left  in  the  soil  by  the  bacteria 
which  lived  with  the  first  crop. 
For  this  reason,  clover  is  often  grown  on  land  in  which  it  is  pro- 
posed to  plant  corn,  the  nitrogen  left  in  the  soil  thus  giving  nour- 
ishment to  the  young  corn  plants.  The  annual  yield  of  the  average 
farm  may  be  greatly  increased  by  this  means. 

Forms  of  Roots  and  their  Relation  to  the  Life  of  the  Plant.  — 
Roots  assume  various  forms.  The  form  or  position  of  the  root  is 
usually  dependent  on  the  needs  of  the  plant,  the  roots  acting  to 
help  it  succeed  in  certain  localities. 

Food  Storage.  —  The  use  to  the  plant  of  the  food  stored  in  the 
taproot  may  be  understood  if  we  think  of  the  life  history^  of  the 
parsnip.  Such  a  plant  produces  no  seed  until  near  the  end  of 
the  second  year  of  its  existence.     After  forming  seeds  it  dies.     The 


Tubercles  on  clover  roots. 


96 


BOTANY 


food  stored  in  its  root  enables  it  to  get  an  early  start  in  the  spring, 
so  as  to  be  better  able  to  produce  seeds  when  the  time  comes. 


Cross  section  of  parsnip.  The 
cortex  (C.)  is  given  up  almost 
entirely  to  the  storage  of 
food.  Note  the  medullary 
rays  (M.R,)  which  radiate 
from  the  center  of  the  wood 
iW.). 


Fascicled  roots  (dahlia) ;  fibrous  roots  which 
have  become  thickened  with  stored  food. 


Examples   of  other   roots  storing   food  nre  carrot,   radish,  yam, 

sweet  potato,  etc.  Demonstration.  —  Test  a  cross  section 

of  the  parsnip  root  with  iodine.  In 
which  part  of  the  root  is  starch  stored? 
Test  another  cross  section  with  nitric 
acid  and  ammonia.  Which  part  of  the 
root  contains  stored  food? 

Water  Roots.  —  In  the  duckweed,  a 
plant  living  in  water,  the  roots  are  short 
and  contain  few  root  hairs.  The  water 
supply  is  so  great  that  few  root  hairs 
have  been  called  forth.  The  water  hya- 
cinth is  another  example  of  slight  de- 
velopment of  roots.  The  plant  is 
buoyed  up  by  the  water  and  does  not 
need  strong  roots  to  held  it  firm. 

Adventitious  Roots.  —  Roots  are 
often  developed  in  unusual  places. 
Roots  coming  out  thus,  as,  for  example, 
on  the  stem,  are  called  adventitious. 
Such  roots  are  developed  along  the 
stem  of  many  climbing  plants.    Exam- 

j ,      ine  and  draw  the  roots  of  English  ivy. 

See  how  many  other  common  wild 
climbers  develop  adventitious  roots. 


Corn  roots,  showing  prop  roots  devel- 
oped at  first  node  above  grouad. 


ROOTS  AND  THEIR  WOUK  97 

Some  plants,  as  strawberry,  couch  grass,  and  many  others,  develop  new 
plants  by  striking  root  at  any  point  on  the  reclining  stem  where  it  touches 
the  ground.  This  fact  is  made  of  use  by  practical  gardeners  in  the  layering 
of  plants. 

Examine  the  Indian  corn  for  another  kind  of  adventitious  root.  Here 
they  serve  as  props  for  the  tall  stem.  In  the  young  seedlings  of  corn,  notice 
how  early  these  roots  develop.  Also  notice  the  manner  in  which  they  arise 
on  the  stem. 

Air  Roots.  —  In  tropical  forests,  where  the  air  is  always  warm  and  moist, 
some  plants  have  come  to  live  above  the  soil  on  the  trunks  of  trees,  or  in 
other  places  where  they  can  get  a  favorable  foothold.  Such  plants  are  called 
epiphytes  or  air  plants.  The  tropical  orchid  seen  in  our  greenhouses  is  an 
example.  Examine  the  roots  of  such  a  plant.  Notice  how  thick  they  are. 
They  are  usually  provided  with  a  spongy  tissue  around  the  outside  which 
has  the  function  of  absorbing  water. 

Parasitic  Roots.  —  A  few  plants  live  on  other  living  plants,  and  develop 
by  the  aid  of  nourishment  taken  at  their  expense.  Such  a  plant  or  animal  is 
called  a  parasite.  The  plant  or  animal  on  which  the  parasite  lives  is  called  the 
host.  The  mistletoe  is  an  example  of  a  parasitic  plant.  An  examination  of 
its  roots  shows  that  they  have  bored  their  way  into  the  stem  of  the  host. 
These  roots  not  only  penetrate  the  bark  but  push  toward  the  center  of  the 
tree,  taking  nourishment  from  the  cells  there.  The  dodder  is  another  seed- 
bearing  plant  which  has  this  habit.  Dodder  produces  from  seed,  but  is 
unable  to  live  alone  after  it  has  passed  the  seedling  stage,  and  will  die  if  it 
cannot  find  a  suitable  host.  It  is  found  on  many  common  weeds,  as  jewel 
weed  and  golden-rod.  Many  of  the  lower  plants  live  as  parasites,  among 
them  being  mildew,  rusts,  and  smuts  found  on  roses,  grain,  and  corn. 

Reference  Books 
for  the  pupil 

Andrews,  Botany  All  the  Year  Round.     Chap.  II.     American  Book  Company. 
Goff  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chaps.  IX,  XI,  XII.     Ginn  and  Company. 
Coulter,  Plant  Studies,  Chap.  V.     D.  Appleton  and  Company. 
Stevens,  Introduction  to  Botany,  pages  31-44.     D.  C.  Heath  and  Company. 

FOR   THE   TEACHER 

Goodale.     Physiological  Botany.     American  Book  Company. 

Gray,  Structural  Botany,  pages  27-39,  56-64.     American  Book  Company. 

Keraer-Oliver,  Natural  History  of  Plants.     Henry  Holt  and  Company. 

Setmer-Moor,  Practical  Plant  Physiology.     The  Macmillan  Company. 

Green,  An  Introduction  to  Vegetable  Physiology,  Chaps.  V.  VI.     J.  and  A.  Churchill. 

MacDougal,  Plant  Physiology.     Longmans,  Green,  and  Company. 

hunter's  BIOL.  —  7 


VIII.    BUDS  AND   STEMS 


Structural  Differences  between  the  Stem  and  the  Root.  —  Wash  carefully 
the  earth  from  the  roots  of  a  pea  seedling  that  you  have  grown  in  the 
laboratory.  Try  to  make  out  the  following  points:  (1)  note  the  differences 
in  color  between  the  stem  and  roots;  (2)  compare  the  manner  in  which  the 
root  and  stem  give  off  lateral  branches.  Notice  that  the  leaves  and  lateral 
branches  from  a  stem  are  more  or  less  regular  in  position,  while  the  small 
roots  have  no  regular  method  of  leaving  the  primary  root.  The  places  on 
the  stem  where  leaves  are  given  off  are  known  as  nodes,  the  part  of  the 
stem  between  being  called  an  internode. 

In  a  growing  stem  of  any  woody  plant,  notice  the  end  of  the 
stem ;  the  bud  at  the  termination  is  a  future  stem.  It  is  well  for 
us  to  remember  that  a  stem  is  a  developed  bud,  as  we  shall  see 
when  we  take  up  the  work  on  the  bud  more  in  detail. 

One  difference  which  is  very  noticeable  between  the  stem  and 
the  root  is  the  color,  the  young  root  being  whitish  or  gray,  and 

the  young  stem  being 
green.  The  following  ex- 
periment will  serv^e  to 
explain  this  difference:  — 

Effect  of  Absence  of  Light 
on  Young  Plants.  —  Plant 
some  peas  in  sawdust  within 
a  box,  or  wide-mouthed  bot- 
tle which  has  been  previously 
blackened  so  that  no  light  is 
admitted  to  the  interior. 
Grow  some  of  the  same  seed 
in  a  box  alongside  the  covered 
material,  giving  each  the  same 
amount  of  heat  and  moisture. 
After  the  young  plants  have 
grown,  take  one  out,  compare 

it  with  the  ones   grown  in   the   light,   and   note   the  difference  in  color. 

Might  the  absence  of  light  account  for  the  color  of  the  root? 

The  seedlings  which  have  been  grown  in  darkness  show  some 
other  interesting  conditions.  The  stems  are  long  and  more  or 
less  reclining  on  the  sawdust.  The  leaves  are  hardly  worthy  of 
the  name,  being  reduced  to  little  scales.     We  know  that  they  are 

98 


A  pocket  garden  which  has  been  kept  in  complete 
darkness  for  several  weeks.  Notice  the  condition 
of  stems  and  leaves. 


BUD^  AND   STEMS 


99 


modified  leaves  because  they  come  out  on  the  stem  in  the  position 
taken  by  leaves.  The  stem  of  the  plant  grown  in  the  darkness  is 
much  longer  and  thinner  than  the  one  grown  in  the  light.  Can 
you  think  of  any  reasons  for  these  differences  ? 

Effect  of  Light  on  Plants.  —  We  can  explain  the  changed  condi- 
tion of  the  seedling  grown  in  the  dark  only  by  assuming  that  light 
has  some  effect  on  the  protoplasm  of  the  seedling  and  induces 
the  growth  of  the  green  part  of  the  plant.  Numerous  instances 
could  be  given  in  which  plants  grown  in  sunlight  are  healthier 
and  better  developed  as  to  their  green  parts  than  those  in  the 
shady  parts  of  a  garden  or  field.  On  the  other  hand,  some  plants 
thrive  in  the  shade.  Such  plants  are  the  mosses  and  ferns.  Still 
other  plants,  minute  organisms  hardly  visible  to  the  eye,  do  not 
thrive  in  the  light,  and  may  be  killed  by  its  influence.  Such  are 
molds,  mildews,  and  some  bacteria.  It  is  to  be  noticed  that 
such  plants  as  do  not  need  light  are  not  green.  As  a  matter  of 
fact,  the  stem,  which  has  but  little  chlorophyll,  develops  some- 
what more  rapidly  under  conditions  where  it  receives  no  light. 

Heliotropism. — We  saw 
that  the  stems  of  the 
plants  kept  in  the  dark- 
ness did  not  always  lift 
themselves  erect  as  in  the 
case  of  stems  in  the  light. 
If  your  seedlings  have 
been  growing  on  a  win- 
dow sill,  or  where  the  light 
comes  in  from  one  side, 
you  have  doubtless  noticed 
that  the  stem  and  leaves 
of  the  seedlings  incline  in  the  direction  from  which  the  light 
comes.  The  tendency  of  young  stems  and  leaves  to  grow  toward 
sunlight  is  called  'positive  heliotropism. 

The  experiment  pictured  on  the  following  page  shows  this  effect 
of  light  very  plainly.  A  hole  was  cut  in  one  end  of  a  cigar  box 
and  barriers  erected  in  the  interior  of  the  box  so  that  the  seeds 
planted  in  the  sawdust  received  their  light  by  an  indirect  course. 


The  growth  of  young  stems  and  leaves  of  oxalis 
toward  the  light. 


100 


BOTANY 


The  young  seedling  in  this  case  responded  to  the  influence  of  the 
stimulus  of  light  so  as  to  grow  out  finally  through  the  hole  in  the 
box  into  the  open  air.  Make  this  experiment,  and  see  if  you  get 
the  same  result.  Vary  the  apparatus  in  any  manner  you  can,  and 
plant  some  other  seeds  or  grains. 

This  experiment  shows  that  another  factor  besides  gravity  influ- 
ences the  stem  to  grow  upward.     This  growth  of  the  stem  to  the 


Two  stages  in  an  experiment  to  show  that  green  plants  grow  toward  the  light. 


light  is  of  very  great  importance  to  a  growing  plant,  because,  as 
we  shall  see  later,  food-making  depends  largely  on  the  amount  of 
sunlight  the  leaves  receive. 

Structure  of  a  Bud.  —  If  we  cut  a  head  of  cabbage  so  that  the 
knife  blade  cuts  through  the  long  axis  of  the  stem,  we  find  that  the 
stem  is  much  shortened  or  dwarfed,  and  that  the  leaves  are  so 
placed  as  to  cover  it  entirely.  The  cabbage  is  a  big  bud.  If 
we  carry  out  our  definition  of  a  bud,  starting  with  what  we  have 
seen  in  the  cabbage,  we  might  say  that  a  bud  is  a  very  much 
shortened  branch,  or  in  reality  ''  the  promise  of  a  branch." 


BUDS  AND  STEMS 


101 


Cabbage  head  cut  lengthwise  to  show  stem  and  leaves.    Photographed  by  Overton. 

Factors    which    influence 
the  Opening  of  a  Bud.  — A 

bud  responds  to  the  same 
stimuli  that  we  have  seen 
call  a  young  plant  into  ac- 
tive life  from  the  seed.  If 
a  branch  containing  un- 
opened buds  (such  as  horse- 
chestnut  or  willow)  is  placed 
in  water  in  a  moderately 
warm  room,  it  will  respond 
to  the  factors  without  it 
and  begin  to  open.  The 
tips  of  branches,  still  at- 
tached to  the  tree  outdoors, 
may  be  introduced  into  a 
warm  room  through  a  hole 
bored  in  the  window  sash. 

Thpv  will  nnpn  to  hpar  flow-       Blossom  bud  of  NoKv-ay  maple  expandeil.  show- 
iney  Wni  open  lO  Dear  now  .^^  inconspicuous  flowers.     Photographed  by 

ers  and  leaves  during  the         Overton. 


102 


BOTANY 


coldest  months  of  the  year.  The  factors  which  influence  the  ger- 
mination of  seeds  also  act  on  the  bud. 

Position  of  the  Bud  on  the  Stem.  —  The  growth  of  the  stem 
from  the  bud  can  best  be  observed  in  a  very  young  seedling.  If, 
for  example,  we  examine  a  pea  seedling,  it  will  be  seen  that  the 
epicotyl  is,  in  truth,  the  first  bud  of  the  plant.  It  produces  the 
first  stem  and  leaves.  The  position  of  the  most  active  buds  deter- 
mines the  form  of  the  future  tree.  Buds  come  out  at  the  ends  of 
branches  {terminal)  and  at  the  sides  {lateral). 

Deliquescent  Tree.  —  If  you  examine  a  winter  branch  of  the 
apple,  elm,  or  oak  tree,  you  will  find  that  the  lateral  buds  have 


Excurrent  trees  (at  right)  and  deliquescent  tree  (at  left).      In  background  a  row  of  cedars 
which  were  planted  by  birds  roosting  on  a  fence  along  a  roadside. 

developed  more  strongly  and  more  rapidly  than  the  terminal  bud. 
Thus  the  tree  has  come  to  assume  during  its  growth  a  rounded 
shape.  Such  a  tree,  having  a  rather  stout,  short  trunk,  with 
many  low,  spreading,  lateral  branches,  is  said  to  be  deliquescent. 

Excurrent  Tree.  —  If,  on  the  other  hand,  the  terminal  buds  of 
the  tree  get  a  better  supply  of  light,  food,  or  if  other  factors  aid  its 
growth,  the  tree  will  be  tall  and  have  but  one  main  trunk,  such 
as  the  Lombardy  poplar,  and  pines  and  cedars.  Such  a  tree  is 
named  excurrent.     The  picture  shows  trees  of  these  two  shapes. 

Structure  and  Functions  of  the  Parts  of  a  Winter  Twig.  —  The 
best  way  for  us  to  understand  the  growth  of  a  bud  into  a  branch 


BUDS  AND  STEMS 


103 


is  to  compare  the  structures  we 
found  in  the  bud  with  the  markings 
that  we  find  on  the  outside  of  a 
branch.  Let  us  take  for  this  work 
a  winter  branch  of  the  horse- 
chestnut  tree.^  Place  some  branches 
in  water  in  a  warm  room  so  that  we 
may  have  some  opened  buds  to 
look  at  later. 

Laboratory  Suggestions.  —  A  twig  in  its 
winter  condition  shows  the  position  of  the 
buds  very  plainly.  Notice  that  the  ter- 
minal buds  are  larger  than  those  on  the 
sides  of  the  branch.  As  the  twig  grew 
last  year  the  scales  covering  the  outside 
of  the  bud  dropped  off  and  the  young 
shoot  developed  from  the  opened  bud. 
The  scales  which  dropped  off  left  marks 
upon  the  surface  of  the  twig,  which  run 
completely  around  the  twig  at  a  given 
point,  forming  a  little  ring.  These  rings 
tell  the  age  of  the  branch.  Estimate  the 
age  of  the  one  you  hold.  Was  the  growth 
always  the  same  each  year?  How  might 
you  account  for  the  different  rate  of 
growth  in  different  years? 

Just  above  the  lateral  buds  are  marks, 
known  as  leaf  traces,  that  show  the  points 
at  which  leaves  were  attached.  A  care- 
ful inspection  of  the  leaf  traces  reveals 
certain  tiny  scars  arranged  more  or  less 
in  the  form  of  a  horseshoe.  These  scars 
mark  the  former  position  of  bundles  of 
tubes  which  we  have  already  studied  in 
connection  with  roots.  They  are,  in  fact, 
continuations  of  the  same  fibrovascular 
bundles  which  pass  from  the  root  up 
through  the  stem  and  out  into  the  leaves, 
where  we  see  them  as  the  veins  which  act 
as  the  support  of  the  soft  green  tissues 
of  the  leaf.  The  most  important  use 
to  the  plant  of  the  fibrovascular  bundles 
is  the  conduction  of  fluids  from  the  roots  to 
the  leaves  and  from  the  leaves  to  the  stem 
and  root.  The  position  of  the  leaf  traces 
on  the  branch  give  us  a  clew  as  to  the 
appearance  of  the  leafy  tree.  If  we  find 
the  leaf  traces  oppositely  placed,  then  we 
know  that  the  leaves  and  buds,  which 


Three-year-old  apple  branch,  showing 
terminal  and  lateral  buds  and  bud 


scars. 


See  Hunter  and  Valentine,  Manual,  page  25. 


104 


BOTANY 


give  rise  to  lateral  branches,  had  a  very  definite  arrangement  in  pairs  at  the 
nodes.  Such  are  the  maple  or  horse-chestnut.  If,  on  the  other  hand, 
the  leaf  traces  are  placed  alternate  to  each  other,  we  can  picture  a  tree  with 
much  less  regularity  in  the  position  of  leaves  and  lateral  branches,  as  in  the 

apple,  beech,  and  elm. 

The  very  tiny  scars,  which  look  like  little  cracks 
in  the  bark,  are  very  important  organs,  especially 
during  the  winter  season,  for  they  are  the  breathing 
lioles  of  the  tree.  A  tree  is  alive  in  winter,  although 
it  is  much  more  active  in  the  warm  weather.  Oxi- 
dation takes  place  much  more  rapidly  in  the  summer 
because  the  plant  is  growing  rapidly,  and  more  fuel 
is  consumed  to  release  the  energy  needed  for  growth. 
We  shall  see  later  that  the  leaves  are  the  chief 
Ijreathing  organs  of  the  plant.  But  all  the  year 
round  oxygen  is  taken  in  by  means  of  the  lenticels, 
as  the  breathing  holes  in  the  trunk  and  branches  of 
a  tree  are  called.  Notice  whether  the  distribution 
of  the  lenticels  is  regular  over  the  surface  of  the 
branch.  Notice  also,  that  some  of  the  lenticels  have 
become  split  in  the  growth  of  the  tree  so  as  to  appear 
as  long  cracks. 

In  the  twig  of  the  horse-chestnut  another  scar 
will  be  found  at  a  point  between  two  branches. 
This  scar  marks  the  place  where  a  cluster  of 
flowers  was  attached.     It  is  called  a  flower  scar. 

Make  a  careful  drawing  of  the  branch,  showing, 
if  possible,  all  the  parts  we  have  discussed.  Make 
careful  labels  for  all  the  parts. 

Adaptations  in  the  Bud  of  Horse-chestnuTo 
—  If  we  now  turn  our  attention  to  the  horse-chestnut 
buds  which  have  been  previously  placed  in  water  to 
open,  we  shall  be  able  to  get  some  notion  of  the 
wonderful  adaptations  of  the  bud,  which  fit  it  for 
its  work. 
In  the  first  place,  a  horse-chestnut  bud  is  covered  with  a  sticky  material. 
Not  only  does  this  covering  keep  out  unwelcome  visitors  which  might  bore 
into  the  bud  and  destroy  the  tender  parts  within,  but  it  also  serves  as  a 
waterproof  covering  against  the  icy  rains  of  the  late  fall  and  early  spring. 
In  the  buds  which  have  not  begun  to  open,  notice  the  overlapping  position 
of  the  scales,  like  the  shingles  on  a  roof.  Of  what  use  might  this  be?  In 
buds  which  have  begun  to  open,  notice  that  not  only  have  the  tiny  green 
leaves  been  protected  by  the  outer  scales,  but  they  have  been  additionally 
WTapped  in  soft,  cottony  substance.  You  can  easily  see  that  the  leaves 
have  been  folded  together  so  that  the  flat  surface  has  had  a  minimum  of 
exposure.  The  young  leaves  are  always  folded  or  rolled  up  in  the  bud. 
Two  purposes  are  thus  served,  protection  from  frost  and  from  drying  by 
little  exposure  of  the  delicate  surface,  and  economy  of  space  by  means  of 
the  tight  and  compact  stowing  away  of  the  parts  thus  folded.     This  ar- 


Twig,  showing  knot  (K) 
and  lenticel  (L). 


BUDS  AND  STEMS 


105 


rangement  of  leaves  within 
the  bud  is  known  as  vernation. 
An  interesting  piece  of  field 
and  laboratory  work  is  the 
comparison  of  vernation  in  a 
number  of  different  buds. 
Those  of  the  wild  cherry,  birch, 
European  walnut,  snowball, 
lilac,  and  tulip  tree  are  of  in- 
terest for  this  purpose. 

Why  buds  are  Covered. — 
When  we  consider  that  most 
of  our  earliest  green  leaves 
come  from  opening  buds  in 
the  early  spring,  the  impor- 
tance of  a  protective  cover- 
ing is  well  seen.  Nevertheless 
buds  are  frozen  time  and  again 
during  the  cold  weather,  only 
to  thaw  out  again  without  in- 
jury to  the  plant.  Sudden 
changes,  however,  do  much 
harm.  Some  buds  do  not  open 
during  mild  winter  weather 
when  temperature  conditions 
are  seemingly  favorable;  a 
definite  length  of  growth  seems 
in  that  case  to  be  necessary. 
During  warm  weather  plants 

give  rise  to  buds  which  are  devoid  of  protective  scale  leaves.    Such  is  also 
noticed  in  tropical  forms,  which  are  not  called  upon  to  meet  rigorous  cli- 
matic   conditions.     We    have    now 
learned  something  about  the  outside 
markings  of  a  branch.^ 

Let  us  turn  our  attention  to  the  in- 
ternal structure  of  the  horse-chestnut 
stem  to  see  how  the  parts  within  are 
adapted  to  perform  the  work  which 
they  do. 

Study  of  a  Dicotyledonous  Stem.  — 
In  the  cross  section  of  horse-chestnut 
twig,  notice  the  innermost  part,  the 
pith.  See  if  it  is  as  tough  as  the  wood 
of  the  stem.  About  what  proportion 
of  the  cross  section  is  occupied  by 
the  wood?  Everything  outside  of  the 
wood  is  collectively  known  as  the 
Section  across  a  young  twig  of  box  elder,  bark.  It  is  made  up  of  three  layers, 
showing  the  four  stem  regions;  e,  epi-  Pull  off  outer  layer;  notice  Its  color, 
dermis,  represented  by  the  heavy  bound- 
ing hne;  c.  cortex;  w,  wood;  p,  pith.  ^  See  Hunter  and  Valentine,  Manual. 
(From  Coulter,  Plant  Relations.)                   page  32. 


Opening  bud  of  horse-chestnut;  L.,  leaves;  L.S., 
leaf  scar;  S.,  scalelike  leaves  which  cover  bud. 


106 


BOTANY 


Compare  it  with  the  layer  just  under  it  as  to  color.  How  does  the  inner 
brown  layer  compare  with  the  others  in  thickness?  This  inner  layer  is 
called  the  bast.  It  is  made  up  largely  of  long,  tough  cells,  somewhat  like 
fibers  in  appearance. 

Notice  the  lines  which  radiate  from  the  pith  to  the  bark  or  cortex. 
They  are  called  medullary  rays. 

Compare  a  cross  section  of  this  stem  with  an- 
other made  just  above,  where  last  year's  bud  w^as 
located.  What  differences  do  you  find  in  the 
two  cross  sections  ?  Show  by  means  of  a  drawing 
the  structure  of  a  horse-chestnut  stem.  This 
may  be  taken  as  a  type  of  dicotyledonous  stem. 
Study  of  a  M onocotyledonous  Stem.  —  Compare 
the  above  section  with  that  of  a  monocotyledon, 
a  piece  of  cornstalk,  for  example.  Notice  that 
in  the  corn  the  whole  stalk  is  more  or  less  pithy 
and  that  the  w^ood  is  scattered  through  the  pith 
in  the  form  of  structures  which  look  like  little 
dots.  Cut  a  piece  of  dry  cornstalk  lengthwise, 
and  you  will  find  that  these  dots  are  the  ends  of 
long  stringy  threads.  If  the  longitudinal  section 
be  made  through  a  node  of  the  cornstalk,  some 
of  these  long  structures  will  be  found  to  curve 
outward  at  the  node  to  enter  the  leaf,  where  they 
can  be  followed  as  veins.  The  threads  are  the 
same  structures  that  we  have  seen  as  the  little 
dots  in  the  leaf  scar  of  the  horse-chestnut  twig, 
the  fibrovascular  bundles.  They  are  composed 
of  bundles  of  very  tiny  tubes,  supported  by  other 
thick-walled,  tough,  woody  cells,  which  give  me- 
chanical support  to  the  tubes.  Notice  that  the 
exterior  of  the  corn  stem  is  composed  of  a  great 
number  of  these  bundles,  which  have  grown  close 
together  and  become  harder  and  thicker.  This 
outer  covering  of  the  cornstalk  is  called  a  rind. 
Of  what  use  might  the  rind  be  to  the  stem  ? 

Structure  of  Fibrovascular  Bundle  in  a  Mono- 
cotyledonous  Stem. — The  stem  of  a  monocotyledon 
consists  largely  of  pith,  with,  as  we  have  seen, 
slender  bundles  of  wood  inclosing  hollow  cells 
placed  end  to  end  to  form  ducts.  These  are  col- 
lected around  the  outer  part  of  the  stem,  thus 
gi^^ng  better  support  to  the  whole  stem. 

A  single  fibrovascular  bundle  in  a  cross  section 
under  the  microscope  shows  the  following  arrange- 
ment. Around  the  outside  of  the  bundle  is  a 
collection  of  thick-walled,  w^oody  cells.  These 
cells  serve  to  support  the  bundle.  Inside  of  these 
cells  are  found  a  number  of  tubes  of  different 
diameters,  some  for  conduction  of  water,  others 
for  air,  and  still  others  for  liquid  food  material  sent  down  from  the  leaves. 
All  of  these  tubes  were  formed  by  the  elongation  of  certain  cells  of  the 
bundle  which  in  their  growth  have  divided  so  as  to  form  a  string  of  cells. 
The  contents  of  some  of  these  cells  die ;  thus  a  hollow  tube  of  cellulose  re- 
mains, which  admits  the  passage  of  material  from  one  level  of  the  stem  to 


Longitudinal  section  of  corn- 
stalk, showing  some  of 
the  fibrovascular  bundles 
passing  outward  at  the 
node  just  above  the  roots. 


BUDS   AND  STEMS 


107 


another  through  the  open  ends  of  the  cells.  We  find  the  conducting  tubes 
have  quite  different  functions :  Some  carry  soil  water  and  air  up  the  stem, 
while  others  take  food  material  down 
toward  the  roots.  As  the  bundles  grow  they 
elongate  rapidly,  but  are  limited  in  their 
growth  outward  by  the  hard- walled,  woody 
cells.  An  old  stem  of  a  monocotyledon  con- 
tains more  bundles  than  does  a  young  stem, 
the  bundles  growing  out  into  the  leaves. 


Monocotyledonous  fib  ro  vascular 
bundle;  p/i,  region  in  which  food 
passes  down;  d,  woody  portion 
or  bundle  ducts  which  carry  air 
and  water;  p,  pith  cell. 

Summary.  — A  stem  of 
corn  contains  pith,  dead 
tissue  which  is  the  original 
soft;  spongy  material  out 
of  which  the  stem  is 
built,  and  a  great  mass  of 
woody  cells,  many  of  them 
tough  and  fiberlike,  serv- 
ing to  support  the  stem; 
others  are  long  cells,  hol- 
low and  end  to  end,  form- 
ing tubes  which  connect 
the  roots  with  the  leaves,  and  through  which  fluids  pass  in  both 

directions. 

The  stem  of  corn  also  contains  a  supply  of  stored  food.  Some 
of  the  cells  of  the  pith  store  food,  which  is  often  being  made  faster 
than  it  can  be  used  by  the  plant.  Many  monocotyledonous  trees 
which  live  for  long  periods  of  time  store  food  in  large  quantities 
in  the  trunk.     The  sago  palm  is  an  example. 


Palms  and  palmettos;    typical  monocotyledonous 
plants.    Scene  on  Indian  River,  Florida. 


108 


BOTANY 


Transverse  section  of  a  stem  of  burdock, 
showing  fibrovascular  bundles  not  com- 
pletely united  into  a  ring. 


Young  Monocotyledonous  Stem.  —  Almost  the  entire  stem  of  a  very 
young,  green  monocotyledon  is  composed  of  soft,  thin-walled  cells.     These 

are  the  cells  making  up  the  paren- 
chyma (parent  tissue.)  Later  in 
the  life  of  the  stem  their  contents 
are  used  up  by  the  plant,  and  we 
find  them  empty  and  dry  in  the  sec- 
tion of  cornstalk.     In  some  mono- 

J     til^^  :J^^fe        I       cotyledonous     stems     their     walls 

"^:    •^SSL  *'-**^.*v*.    \       become  hard,  while  in  other  cases, 

as  in  the  bamboo,  they  entirely  dis- 
appear. 

Structure  op  a  Young  Dicoty- 
ledonous Stem.  —  In  the  stem 
of  a  young  dicotyledon  the  pith  is 
found  to  occupy  relatively  a  small 
space  in  the  middle  of  the  section. 
This  pith  is  composed  of  the  paren- 
chyma cells  such  as  we  found  in  the 
cornstalk.  Surrounding  the  pith  is 
the  wood.     The  wood  consists  (in 

the   cross  section)  of  the  ends  of  many  tubes  and  the  woody  walls  of 

supporting  cells  which  occupy  that 

area.     If    the    section    is    several 

years  old,  we  shall  find  a  definite 

ring  in  the  wood  for  each  year's 

growth. 

Medullary     Rays.  —  Radiat- 
ing from  the  center  of  the   stem 

outward  are  found  a  number  of 

tiny  lines.     These  are  more  promi- 
nent  in   stems  of    older    growth. 

The  medullary  rays,  as  they  are 

called,  are  seen  to  begin   at  the 

pith   and   pass   out   to   the  bark. 

They  are,  indeed,  formed   of  the 

pith.   They  are  part  of  the  original 

parenchyma  which  at  first  formed 

a  large  part  of  the  whole  stem.    As 

the  stem  grew  in  size,  fibrovascular 

bundles  appeared.     These  bundles 

were   not   scattered    through   the 


Section  across  a  twig  of  box  elder  three  years 
old,  showing  three  annual  growth  rings,  in 
the  vascular  cylinder.  The  radiating  lines 
(m),  which  cross  the  wood  {w),  represent  the 
pith  rays,  the  principal  ones  extending  from 
the  pith  to  the  cortex  (c).  (From  Coul- 
ter, Plant  Relations.) 


stem,  but  were  arranged  more  or  less  completely  in  a  circle.     Growth  of 
these  woody  bundles  took  place  along  the  outer  edge.    This  caused  the 


BUDS  AND  STEMS 


109 


bundles  ultimately  to  unite  along  the  outer  edge  because  of  more  rapid 
growth  in  that  region.  This  rapidly  growing  area,  which  extends  com- 
pletely around  the  stem  under  the  bark  as  a  hollow  cylinder,  is  called  the 
cambium  layer.  All  growth  takes  place  from  that  part  of  the  stem.  As  the 
bundles  squeezed  together  in  their  growth,  the  pith  or  parenchyma  became 
compressed  into  thin  plates,  the  edges  of  which  are  seen  in  the  cross  section. 
We  call  these  plates  the  medullary  rays. 

Microscopic  Structure  of  a  Fibrovascular  Bundle  in  the  Dicoty- 
ledonous Stem. — The  structure  of  one  of  the  young  bundles  in  a  young 
dicotyledonous  stem  is  somewhat  as  seen  in  the  illustration.  The  bundle 
is  composed  of  two  areas.  The  inner  area,  directed  toward  the  middle  of 
the  stem,  is  made  up  of  woody,  thick-walled  cells,  which  support  and  in 
some  cases  form  part  of  the  walls  of  the  tubes  which  carry  the  soil  water  up 
the  tree.  These  tubes  differ  considera- 
bly in  size,  the  larger  ones  being  formed 
during  the  more  rapid  spring  growth  of 
the  bundle.  The  outer  part  of  the  bun- 
dle, which  is  separated  from  the  inner 
part  by  the  cambium  layer,  is  quite  dif- 
ferent in  structure  from  the  inner  part. 
It  is,  in  fact,  growing  toward  the  outside 
and  is  forming  the  inner  layer  of  the  bark. 
The  cells  of  the  cambium  layer  are  much 
softer  and  have  thinner  walls  than  those 
of  the  wood,  because  they  are  filled  with 
protoplasmic  material  and  are  constantly 
dividing  to  form  new  cells. 

Most  of  the  cells  of  the  inner  bark 
are  extremely  tough  and  fibrous.  Be- 
tween the  bast  fibers,  as  the  tough  cells 
are  called,  are  found  numerous  elongated  cells  joined  end  to  end,  the  ends 
of  each  cell  being  full  of  little  holes.  These  are  the  sieve  tubes  (or  soft  bast 
cells) ;  they  serve  as  a  channel  for  the  sap  or  food  materials  which  come 
down  from  the  leaves  toward  the  roots.  This  region  of  the  stem  also  stores 
considerable  food  in  a  form  suitable  for  the  use  of  the  stem. 

As  growth  proceeds,  the  cambium  layer  constantly  grows  outward,  and 
each  new  year  new  fibrovascular  bundles  are  added  to  supply  the  new 
leaves  and  branches  of  that  season.  This  accounts  for  the  fact  that  in 
cross  sections  of  small  twigs  some  of  the  medullary  rays  appear  to  start 
from  the  pith,  some  from  the  outer  edge  of  the  first  annual  ring,  and  still 
more  from  each  succeeding  outer  ring. 

The  outer  bark  of  the  tree  is  protective.  The  cells  are  nearly  all  dead, 
and  the  heavy  woody  skeletons  keep  out  cold  and  dryness,  as  well  as  pre- 
vent the  evaporation  of  the  fluids  within.    Most  trees  are  pro\nded  with  a 


Fibrovascular  bundle  of  a  dicotyledon; 
ph,  region  of  sieve  tubes;  c,  cam- 
bium; d,  duct;  and  /.  fibers  of  the 
woody  part  of  the  bundle. 


no 


BOTANY 


layer  of  corky  cells,  which  serve  this  purpose.*    The  experiment  here  illus- 
trated shows  this. 

Select  two  potatoes  of  equal  weight  and  peel  the  skin  from  one.  Place 
the  pared  potato,  with  the  parings,  in  one  pan  of  the  scales  and  the  other 
potato  in  the  other  pan;  it  will  be  found  that  the  pared  potato  loses 
weight  very  rapidly.  A  reco'^d  of  this  loss  of  weight  should  be  kept  and 
the  results  noted  in  tabular  order.  Of  what  use  is  the  epidermis  to  the 
potato?  2 

Passage  of  Fluids  up  M onocotyledonous  and  Dicotyledonous  Stems. —  Use 
old  seedlings  of  Indian  corn  for  the  monocotyledonous  stem.  Cut  off  the  stem 
close  to  root  and  place  it  in  a  solution  of  eosin  or  red  ink.     Place  some  cut 


Experiment  to  show  that  the  skin  of  the  potato  retards  evaporation. 

dicotyledonous  stems  in  red  ink.  Garden  balsam,  which  can  be  grown  in 
the  hothouse  or  laboratory,  is  the  most  transparent.  Impatiens  and  sun- 
flower are  also  good.  Leave  them  in  the  solution  in  a  sunny  room  for  one 
day.  In  all  the  above  cases  the  colored  material  is  found  to  move  up  the 
stem  and  into  the  leaves  and  flowers.  Cut  some  of  the  above  stems  and 
examine  them  closely  to  see  where  the  most  red  ink  is.  Compare  the  distri- 
bution of  bundles  in  stems  with  their  distribution  in  the  taproot. 

Passage  of  Fluid  up  and  down  the  Stem.  —  From  the  above 
experiments  it  is  evident  that  the  course  taken  by  water  in  its 
course  up  the  stem  is  confined  to  the  collections  of  woody  tubes 
which  we  call  the  fibrovascular  bundles.     In  the  stem  of  a  mono- 

J  The  extreme  outside  layer  of  cells,  as  in  the  root,  is  known  as  the  epidermis. 
It  is  often  not  seen  in  old  stems. 

2  See  Hunter  and  Valentine,  Manual,  page  239. 


BUDS   AND   STEMS 


111 


cotyledon  we  see  the  cut  ends  of  the  bundles  in  a  cross  section 
scattered  through  the  pith.  In  the  dicotyledonous  stem  the 
pathway  of  the  colored  fluid  is  much  more  definite  with  reference 
to  the  outside  of  the  stem.  Try  to  follow  the  lines  out  into  the 
leaves  or  buds,  tracing  the 
course  exactly. 

If  the  following  experiment  is 
made,  it  will  be  found  that  fluid 
passes  not  only  up  the  stem  but 
also  down  the  stem. 

N.B.  This  experiment  should 
be  started  several  (at  least  two) 
weeks  in  advance. 

Place  willow  twigs  in  a  glass 
of  water.  After  a  few  days  roots 
begi  n  to  gro w .  Where  do  the  roots 
appear  ?  After  they  have  grown 
several  da3^s  (until  the  roots  are 
one  inch  in  length)  girdle  a 
twig  by  removing  the  bark  in  a 
ring  about  one  inch  in  width. 
After  a  time,  roots  appear  above 
the  cut  area  and  grow  down  to- 
ward the  water.  The  lower  roots 
below  the  girdled  area  die. 

This  experiment  shows  us 
that  the  passage  of  food  ma- 
terials evidently  takes  place 
in  a  downward  direction  just 
outside  the  wood  in  the  layer 
of  bark  which  contains  the 
bast  fibers  and  sieve  tubes. 
Food  substances  are  also  con- 
ducted to  a  much  less  extent 
in  the  wood  itself,  and  food 
passes  from  the  inner  bark  to 
the  inside  of  the  tree  by  way 
of  the  pith  plates  or  medullary  rays.  This  can  be  proved  by 
testing  for  starch  in  the  medullary  rays  of  young  stems.  It  is 
found  that  much  starch  is  stored  in  this  part  of  the  tree  trunk. 
This  experiment  with  the  willow  explains  why  it  is  that  trees  die, 
when  girdled  so  as  to  cut  the  sieve  tubes  of  the  inner  bark.     The 


Apple  twigs  split  to  show  the  course  of  sap. 


112 


BOTANY 


food  supply  is  cut  off  from  the  protoplasm  of  the  cells  in  the 
part  of  the  tree  below  the  cut  area. 

In  what  Form  does  Food  pass  through  the  Stem?  —  We  have 
already  seen  that  materials  in  solution  (those  substances  which 
will  dissolve  in  the  water)  will  pass  from  cell  to  cell  by  the  pro- 
cess of  osmosis. 

Experiment.  —  Partly  fill  one  thistle  tube  with  starch  and  water,  and  an- 
other with  sugar  and  water.  Tie  over  the  end  of  each  tube  a  piece  of  parch- 
ment paper.    Place  both  test  tubes  under  water  in  a  dish.    After  twenty-four 


Experiment  showing  the  osmosis  of  sugar  (right-hand  tube)  and  non-osmosis  of  starch 

(left-hand  tube). 

hours,  test  the  water  in  the  dish  for  starch,  and  then  for  sugar.  We  find 
only  the  sugar,  which  has  been  dissolved  by  the  water,  can  pass  through 
the  membrane. 

Digestion.  —  As  we  shall  see  later,  the  food  for  a  plant  is  manu- 
factured in  the  leaves.  Much  of  this  food  is  in  the  form  of  starch. 
But  starch,  being  insoluble,  cannot  be  passed  from  cell  to  cell  in 
a  plant.  It  must  be  changed  to  a  soluble  form.  It  is  changed 
by  a  process  known  as  digestion.  We  have  already  seen  that 
starch  was  changed  to  grape  sugar  in  the  corn  by  the  action  of  a 
substance  (a  digestive  ferment)  called  diastase.  This  process  of 
digestion  seemingly  may  take  place  in  all  living  parts  of  the  plant, 
although  most  of  it  is  done  in  the  leaves. 


BUDS   AND   STEMS 


113 


The  food  material  may  be  passed  in  a  soluble  form  until  it  comes  to  a 
place  where  food  storage  is  to  take  place,  then  it  can  be  transformed  to  an 
insoluble  form  (starch,  for  example) ;  later,  when  needed  by  the  plant  in 
growth,  it  may  again  be  transformed  and  sent  in  a  soluble  form  through 
the  stem  to  the  place  where  it  will  be  used.  The  processes  by  which  starch 
is  mada  soluble  in  the  stem  in  the  form  of  sugar  and  then  changed  back 
again  to  starch  are  but  little  understood. 

Building  of  Proteids.  —  Another  very  important  food  sub- 
stance stored  in  the  stem  is  protdd.  Of  the  building  of  proteid 
little  is  known.  We  know  it  is  an  extremely  complex  chemical 
substance  which  is  made  in  plants  from  compounds  containing 
nitrogen,  the  nitrates  and  compounds  of  ammonia  received 
through  the  roots  from  the  organic  matter  contained  in  the  soil, 
in  combination  with  sugars  or  starches  of  the  plant  body. 

Some  forms  of  proteid  substance  are  soluble  and  others  insoluble  in  water. 
White  of  egg,  for  example,  is  slightly  soluble  but  can  be  rendered  insoluble 
by  heating  it  so  that  it  coagulates.  In  a  plant, 
soluble  proteids  pass  down  the  sieve  tubes  in  the 
bast  and  then  may  be  stored  in  the  bast  or 
medullary  rays  of  the  wood  in  an  insoluble  form. 

What  forces  Water  up  the  Stem.  —  We 
have  seen  that  the  process  of  osmosis  is  responsi- 
ble for  taking  in  soil  water,  that  the  enormous  ab- 
sorbing surface  exposed  by  the  root  hairs  makes 
possible  the  absorption  of  a  large  amount  of 
water.  Frequently  this  is  more  than  the  weight 
of  the  plant  in  every  twenty-four  hours. 

Experiments  have  been  made  which  show  that 
at  certain  times  in  the  year  this  water  is  in  some 
way  forced  up  the  tiny  tubes  of  the  fibro vascular 
bundles.  It  can  be  shown  to  rise  a  few  inches 
in  some  stems  by  a  laboratory  experiment.  This 
is  best  seen  in  the  dahlia  stem.  During  the  spring 
season,  in  young  and  rapidly  growing  trees,  water 
has  been  proved  to  rise  to  a  height  of  nearly  ninety 
feet.    The  force  that  causes  this  rise  of  water  in  stems  is  known  as  root  pressure. 

But  root  pressure  alone  cannot  account  for  the  rise  of  water  (as  in  the 
stems  of  the  big  trees  of  California)  to  a  height  of  several  hundred  feet. 
Other  forces  must  play  a  part  here.  One  way  in  which  the  rise  of  water  can 
be  partly  accounted  for  is  in  the  fact  that  capillary  attraction  may  help  in 
part.     If  you  place  in  a  glass  containing  red  or  other  colored  fluid  three  or 

hunter's   BIOL. — 8 


Diagram  to  show  the  areas  in 
the  stem  through  which 
raw  food  materials  pass 
up  the  stem  and  food 
materials  pass  down 
(After  Stevens.) 


114 


BOTANY 


four  tubes  of  different  inside  diameter,  the  fluid  will  be  found  to  rise  very 
much  higher  in  the  tubes  having  a  smaller  diameter.  This  is  caused  by  cap- 
illarity or  capillary  attraction.  When  we  consider  that  the  tubes  of  the  fibro- 
vascular  bundles  are  very  much  smaller  than  any  we  can  make  out  of  glass, 
it  can  be  seen  that  water  might  rise  in  the  stem  to  some  height  in  tubes  of 
microscopic  diameter. 

Another  suggested  method  for  the  rise  of  water  is  given  in  the  fact  that 
air  is  found  in  some  of  the  tubes  in  the  form  of  bubbles,  and  these  minute 
bubbles  may  help  in  the  ascent  of  water. 

The  greatest  factor,  however,  is  one  which  will  be  more  fully  explained 
when  we  study  the  work  of  the  leaf.  Leaves  pass  off  an  immense  quan- 
tity of  water  by 
evaporating  it 
in  the  form  of 
vapor.  This 
evaporation 
seems  to  result 
in  a  kind  of  suc- 
tion on  the  col- 
umn of  water 
in  the  stem.  In 
the  fall,  after 
the  leaves  have 
gone,  much  less 
water  is  taken  in 
by  roots,  show- 
ing that  an  inti- 
mate relation 
exists  between 
the  leaves  and 
the  root. 

Structure 
of  Wood. — 

Quite  a  differ- 
ence in  color 
and  structure 

is  often  seen  between  the  heart  wood,  composed  of  the  dead  walls 
of  cells  occupying  the  central  part  of  the  tree  trunk,  and  the  sap 
wood,  the  living  part  of  the  stem.  In  trees  which  are  cut  down 
for  use  as  lumber  and  in  the  manufacture  of  various  furniture, 
the  markings  and  differences  in  color  are  not  always  easy  to 
understand. 


Cross  section  through  a  black  oak  showing  heart  wood  and  sap  wood 
and  medullary  rays.    (From  Pinchot,  U.S.  Dept.  of  Agr.) 


BUDS   AND   STEMS 


115 


Methods  of  cutting  Timber.  — 

A  glance  at  the  diagram  of   the 

sections  of  timber  show  us  that  a 

tree  may  be  cut  radially  through 

the  middle  of  the  trunk,  or  tan- 

gentially  to  the  middle  portion. 

Most  lumber  is  cut  tangentially. 

Hence   the  yearly  rings  take  a 

more    or    less    irregular  course. 

The  grain  of  wood  is  caused  by 

the   fibers    not    taking    straight 

lines  in  their  course  in  the  tree  trunk.     In  many  cases  the 

of  the  wood  take  a  spiral  course  up  the  trunk,  or  they  may 


Diagrams  of  sections  of  timber: 
section;'  b,  radial;  c,  tangential. 
Pinchot,  U.S.  Dept.  of  Agr.) 


a,  cross 
(From 


fibers 
wave 


Sections  of  white  pine  wood.    (From  Pinchot,  U.S.  Dept.  of  Agr.) 

outward  to  form  little  projections.     Boards  cut  out  of  such  a 
piece  of  wood  will  show  the  effect  seen  in   many   of  the   school 

desks,  where  the  annual  rings  appear  to  form 
small  elliptical  markings. 

Knots.  —  Knots,  as  can  be  seen  from  the 
diagram,  are  branches  which  at  one  time 
started  in  their  outward  growth  and  were  for 
some  reason  killed.  Later,  the  tree,  continu- 
ing in  its  outward  growth,  surrounded  them 
and  covered  them  up.  A  dead  limb  should 
be  pruned   before  such  growth  occurs.     The 

Section  of  tree  trunk  ,  .  •        i  •     i »  i  i    i 

showing  knot.  markmgs  m   bird  s-eye  maple  are  caused  by 


116 


BOTANY 


adventitious  buds  which  have  not  developed,  and  have  been  over- 
grown with  the  wood  of  the  tree. 

Budding.  —  We  have  said  a  bud  is  a  promise  of  a  branch ;  it  may  be  more, 
the  promise  of  a  new  tree.  If  the  owner  of  an  apple  tree  or  peach  tree 
wishes  to  vary  the  quahty  of  fruit  borne  by  the  tree  he  may  in  the  early  fall 
cut  a  T-shaped  incision  in  the  bark  and  then  insert  a  bud  surrounded  with 
a  little  bark  from  the  tree  bearing  the  desired  fruit,*  The  bud  is  bound  in 
place  and  left  over  the  winter.  When  a  shoot  from  the  imbedded  bud  grows 
out  the  following  spring  it  is  found  to  have  all  the  charac- 
ters of  the  tree  from  which  it  was  taken.  This  process  is 
known  as  budding. 

Grafting.  —  Of  much  the  same  nature  is  grafting.  Here, 
however,  a  small  portion  of  the  stem  of  the  closely  allied  tree 
is  fastened  into  the  trunk  of  the  growing  tree  in  such  a  man- 
ner that  the  two  cut  cambium  layers  will  coincide.  This  will 
allow  of  the  passage  of  food  into  the  grafted  part  and  insure 
the  ultimate  growth  of  the  twig.  Grafting  and  budding  are 
of  considerable  economic  value  to  the  fruit  grower,  as  it  en- 
ables him  to  produce  at  will  trees  bearing  choice  varieties 
of  fruit.  Over  fifty  methods  of  grafting  are  described  in 
agricultural  books.  Those  more  successfully  used  are  the 
cleft  graft  and  the  so-called  whip  graft .^ 
Forestry.  —  The  American  forests  have  long  been  our  pride.  Not  only 
do  they  form  the  source  of  a  very  great  industry,  but  what  is  still  more  vitcl 
to  us,  they  protect  the  source  of  much  of  our  water  supply.  They  also 
serve  as  a  protection  against  wind,  floods,  and  moving  sands.  In  Germany, 
especially,  this  relation  of  forest  to  water  supply  has  been  for  a  long  time 
recognized,  and  the  German  forester  or  caretaker  of  the  forests  is  well  known. 
In  some  parts  of  central  Europe  the  value  of  the  forests  was  recognized 
as  early  as  the  year  1300  a.d.,  and  many  towns  consequently  bought  up  the 
surrounding  forests.  The  city  of  Zurich  has  owned  forests  in  its  vicinity 
for  at  least  600  years.  In  this  country  only  recently  has  the  importance 
of  preserving  and  caring  for  our  forests  been  noted  by  our  government. 
Now,  however,  we  have  a  Division  of  Forestry  of  the  Department  of  the 
Interior ;  and  this  and  numerous  state  and  university  schools  of  forestry  are 
rapidly  teaching  the  people  of  this  country  the  best  methods  for  the  preser- 
vation of  our  forests.  The  Federal  Government  has  set  aside  a  number  of 
tracts  of  mountain  forest  in  some  of  the  Western  states,  some  forty  reserves 
in  all,  making  a  total  area  of  almost  twice  the  size  of  the  state  of  Pennsyl- 
vania.   New  York  has  established  for  the  same  purpose  the  Adirondack 

^  This  bud  should  be  taken  from  a  tree  of  the  same  species. 

^  For  full  directions  for  budding  and  grafting,  see  Hodge,  Nattire  Study  and  Life, 
pages  169-179,  or  Goff  and  Mayne,  First  Principles  of  Agriculture,  Chap.  XIX. 


A  cleft  graft. 


BUDS  AND  STEMS  117 

I*ark,  with  over  1,000,000  acres  of  timber  land,  and  other  states  are  fol- 
lowing her  example. 

Methods  for  keeping  and  protecting  the  Forests.  —  Forests  should 
be  kept  thinned.  Too  many  trees  are  as  bad  as  too  few.  They  struggle 
with  one  another  for  foothold  and  light,  which  only  a  few  can  enjoy.  Several 
methods  of  renewing  the  forest  are  in  use  in  this  country.  (1)  Trees  may  be 
cut  down  and  young  ones  allowed  to  sprout  from  cut  stumps.  This  is 
called  coppice  growth.  This  growth  is  well  seen  in  parts  of  New  Jersey. 
(2)  Areas  or  strips  may  be  cut  out  so  that  seeds  from  neighboring  trees 
are  carried  there  to  start  new  growth.  (3)  Forests  may  be  artificially  planted. 
Two  seedings  planted  for  every  tree  cut  is  a  rule  followed  in  Europe.  The 
greatest  dangers  are  from  fire,  which  often  devastates  large  areas,  and 
from  careless  cutting. 

The  Economic  Value  of  Trees.  —  Trees  form  a  protective  cover- 
ing for  the  earth's  surface.  They  prevent  soil  from  being  washed 
away  and  they  hold  moisture  in  the  ground.  This  they  do  because 
the  evaporation  of  moisture  through  the  stomata  of  the  leaves  cools 
the  atmosphere,  thus  tending  to  precipitate  the  moisture  in  the 
air.  Without  trees  many  of  our  rivers  might  go  dry  in  summer, 
while  in  the  rainy  season  sudden  floods  would  result.  This  has 
occurred  in  parts  of  Switzerland,  France,  and  in  Pennsylvania, 
where  the  forest  covering  has  been  removed.  In  some  localities 
forests  are  used  as  wind-breaks  and  to  protect  mountain  towns 
against  avalanches.  Thus  in  winter  they  moderate  the  cold,  and 
in  summer  reduce  the  heat  and  lessen  the  danger  from  storms. 
The  nesting  of  birds  in  woods  protects  many  plants  valuable  to 
man  which  otherwise  might  be  destroyed  by  insects. 

Wood  has  great  commercial  importance  as  well.  Even  in  this 
day  of  coal,  wood  is  still  by  far  the  most-used  fuel.  It  is  useful  in 
building.  It  outlasts  iron  under  water,  in  addition  to  being  dura- 
ble and  light.  It  is  cheap  and,  with  care  of  the  forests,  inex- 
haustible, while  our  mineral  wealth  will  some  day  be  used  up. 
Hard  woods  are  chiefly  used  in  house  building  and  furniture  manu- 
facture; the  soft  woods,  reduced  to  pulp,  are  made  into  paper. 
Distilled  wood  gives  alcohol.  Partially  burned  wood  is  charcoal. 
Vinegar  and  other  acids  are  obtained  from  trees,  as  are  tar,  creo- 
sote, resin,  turpentine,  and  other  useful  oils. 

Modified  Stems.  —  Stems,  as  well  as  roots,  may  be  modified  or  changed 
to  adapt  these  parts  of  the  body  to  their  surroundings.     As  we  have  learned 


118 


BOTANY 


by  experiments,  external  forces  act  on  the  organs  of  a  plant  so  as  to  change 
its  appearance  and  often  its  form  and  habit.  A  stem  grown  in  complete 
darkness  is  white  instead  of  green.  The  bleaching  of  the  celery  stems  by 
covering  them  is  a  familiar  example  of  this.  Thus,  in  nature,  forces  which  we 
know  of  as  light,  gravity,  heat,  moisture,  wind,  and  many  other  factors, 
influence  the  plant  in  its  growth.  Let  us  now  examine  some  of  the  examples 
of  modified  stems. 

Stems  Modified  for  Water  or  Food  Storage.  —  Many  stems  store 
large  quantities  of  food.  The  sago  palm  is  an  example  of  such  a  stem.  In 
most  woody  stems  food  is  stored  during  some  parts  of  the  year  and  is  used 
as  the  plant  comes  to  need  it.  In  other  stems  the  conditions  of  life  are  such 
that  the  plant  has  come  to  store  water  in  the  stem.  The  cactus,  which  we 
shall  examine  more  in  detail  later,  is  a  plant  that  has  developed  the  stem 
for  the  storage  of  water,  and  is  so  adapted  to  desert  conditions  as  to  prevent 
the  evaporation  of  water  from  the  plant. 

Underground  Stems;  the  Rootstock.  —  Other  stems  not  only  con- 
tain stored  food  but  run  underground  for  the  protection  of  the  plant.     Such 

a  stem  is  the  rootstock 
of  the  iris.  The  root- 
stock  in  many  respects 
resembles  a  root,  but  can 
be  distinguished  from 
this  part  of  the  plant  be- 
cause the  leaves  come 
out  from  definite  points 
or  nodes  and  because 
true  roots  leave  the  under 
surface.  Some  under- 
ground stems  do  not 
store  food,  but  grow  with 
considerable  rapidity, 
thus  covering  ground  and 
starting  new  outposts  of 
the  plant  at  a  distance 
from  the  original  plants. 
The  pest  called  quick 
grass  or  couch  grass, 
found  in  almost  every 
lawn,  has  such  a  stem.  It  may  be  cut  in  pieces,  but  each  piece  may  strike 
root,  thus  multiplying  the  plant. 

The  Tuber.  —  If  the  underground  stem  becomes  thickened  at  its  end 
and  there  forms  an  enlargement  for  the  storage  of  food,  we  call  such  an 
enlargement  a  tuber.  Its  use  to  the  plant  is  evident  when  a  potato  is 
planted. 


A  rootstock,  an  underground  stem.    Note  the  leaf  scars 
CL.6'.),  the  roots  {R.),  and  the  leaf  stalk  (P.). 


BUDS  AND  STEMS 


119 


A  tuber. 


Note  the  stems  growing  from 
the  eyes  at  one  end. 


IT-  ^^^Y^l^^  ^  ^^^^?.  potato./      Notice   the  marks  or  eyes  on  its  surface. 

Find  a  little  projection  withm  each  eye.     This  is  a  bud.     Immediately  under 

It  you  will  find  a  tmy  scale  which  represents  a  leaf.    Later  we  shall  see  that 

a  bud  on  a  stem  always  has  the  same 

relation  to  a  leaf  as  does  this  bud  to  the 

tiny  scale.    In  other  words,  the  position 

is  the  same  in  each  case,  and  the  struc- 
ture may  be  said  to  be  homologous  to 

that  of  the  bud  and  leaf  of  an  ordinary 

stem. 

Try  to  find  out  the  arrangement  of 

the  leaves  on  the  potato;  they  may  be 

either  opposite  or  alternately  placed  on 

the  stem.    See,  also,  if  you  can  find  the 

point  at  which  the  stem  was  attached 

to  the  parent  plant. 

If  a  potato  is  cut  in  cross  section  it 

will  be  possible  to  find  all  the  parts  of 

a  stem.     The  pith  occupies  the  central 

portion;  around  this  is  the  wood,  which  here  looks  hke  a  dark  band.     Out- 
side the  wood  we  find  the  cortex,  the  potato  being  protected  by  the  rather 

delicate  epidermis. 

Cut  a  potato  and  a  sweet  potato  in  cross 
section;  place  each  in  red  ink  overnight. 
It  will  then  be  easy  to  compare  the  course 
taken  by  fluids  in  passing  up  a  root  and  a 
stem. 

Cut  out  several  eyes  from  healthy  pota- 
toes. From  one  or  two  remove  all  of  the 
flesh  of  the  potato,  and  in  the  other  speci- 
mens leave  food  supply  intact.  Does  the 
stored  food  help  the  young  plant  in  its 
growth  ?  Test  for  food  stuffs  in  the  potato. 
What  foods  are  present? 

Reduced  Stems.  —  In  some  plants  the 
stem  is  so  reduced  as  to  be  almost  lost. 
This  may  be  of  a  distinct  advantage  to  the 
plant  in  enabling  it  to  escape  destruction 
from  enemies.  Such  a  plant  is  the  common 
dandelion,  which,  because  of  its  short  stem, 
escapes  grazing  animals  and  the  knives  of 
lawn  mow^ers.  Many  other  low-lying  weeds 
are  partly  immune  from  dangers  which  be- 
set taller  plants. 
Bulbs.  —  In  bulbs  the  stem  is  covered  with  thickened  leaves,  the  whole 

making  a  compact  and  reduced  plant  which,  because  of  its  stored  food, 

enables  the  plant  to  make  an  early  start  in  the  spring. 

Cut  an  onion  in  longitudinal  sections;  draw,  showing  the  scalelike, 
thickened  leaves,  the  greatly  reduced  stem,  and  the  roots.  Test  for  food 
stuffs.     What  foods  do  you  find  present  in  the  onion  ? 

»  See  Hunter  and  Valentine,  Manual,  page  29. 


Longitudinal  section  of  a  lily  bulb. 
Note  the  much  thickened  leaves, 
and  the  flower  cluster  at  the 
center.  Photographed      by 

Overton. 


120 


BOTANY 


Climbing  Stems.  Field  Work.  —  A  field  excursion  may  be  made  for 
the  purpose  of  obtaining  as  many  kinds  of  climbing  stems  as  possible.  Place 
them  in  one  of  the  following  classes:  — 

(1)  Stems  which  twist  or  twine. 

(2)  Stems  having  roots  as  holdfasts. 

(3)  Stems  having  parts  of  leaves  or  branches  as  holdfasts. 

Stems  may  twist  around  an  object  in  order  to  climb.  Such  a  plant  is 
the  morning  glory.     Here  the  stimulus  which  draws  the  plant  upward  is 

evidently  the  sun.  In  stems  which  make  use  of  this 
method  of  climbing,  it  is  noticed  that  each  stem  twines 
around  the  support  in  a  given  direction,  some  revolving 
with  the  course  of  the  sun,  others  in  the  opposite  direc- 
tion. When  such  a  stem  touches  an  object  during  its  first 
growth,  it  is  immediately  stimulated  to  turn  toward  the 
object  and  coil  around  it. 

Leaves  and  Stems  modified  as  Holdfasts.' — In  the 
common  nasturtium  (TropoBolum)  the  leaves  revolve  in 
much  the  same  manner  as  do  the  stems  mentioned  above. 
This  movement  results  in  some  of  the  leafstalks  fasten- 
ing around  supports,  thus  drawing  the  stem  up. 

Tendrils.  —  In  some  plants  definite  climbing  organs, 
known  as  tendrils,  are  developed.  A  tendril,  which  has 
the  appearance  of  a  much-twisted  stem,  may  be  modi- 
fied from  part  of  a  leaf,  as  an  entire  leaf  or  as  part  of  a 
branch.  Tendrils  have  the  habit  of  at  first  stretching 
out  as  far  from  the  main  stem  as  possible,  then  slowly 
revolving.  After  a  support  is  touched  they  immediately 
coil  around  it  and  then  begin  to  curl  up  somewhat  after 
the  manner  of  a  watch  spring.  This  draws  up  the  stem 
of  wliich  they  are  a  part. 

Examine  the  tendrils  of  wild  grape,  pea,  Virginia 
creeper,  catbrier,  white  bryony,  or  any  others  you  may 
drilT'(T)^*are  ^^^'  ^^tice  the  position  of  the  tendril  on  the  main 
modified  sttp-  stem  and  try  to  decide  of  what  part  of  the  plant  it  is  a 
ules  (parts  of  modification.  Notice  the  suckers  or  disks  at  the  ends  of 
leaves);  Th,  the  tendrils  of  the  Virginia  creeper.  Can  you  discover 
thorn. '  '       their  use? 


Stems  modified  as  Thorns.  —  Leaves  and  parts  of  leaves  maybe  changed 
into  thorns  for  the  protection  of  the  plant.  In  some  instances  the  stem 
becomes  a  spine  or  thorn.     Such  is  the  case  in  the  honey  locust. 

Compare  it  with  the  black  locust,  in  which  a  part  of  the  leaf,  the  stipule, 
becomes  the  thorn.  All  such  modifications  seem  to  result  in  the  better  pro- 
tection of  tender  parts  wliich  might  otherwise  suffer  from  the  attack  of 
animals. 


BUDS  AND  STEMS 


121 


Leaflike  Stems. — An  exami- 
nation of  tlie  hothouse  smilax 
(M yrsiphyllum)  shows  us  that  the 
structures  which  at  first  sight  ap- 
pear to  be  leaves  are  really  green, 
leaflike  branches.  This  we  know, 
because  immediately  below  each 
cladophyll,  as  the  leaflike  branch 
is  called,  we  find  a  tiny  scale,  evi- 
dently the  leaf.  The  cladophyll 
occupies  the  same  position  with 
relation  to  the  leaf  that  a  bud 
which  develops  into  a  lateral 
branch  would  occupy.  Thus  we 
see  it  is  homologous  to  a  branch. 

Roots  and  Stems  as  Food.  — 
Underground  stems  and  roots  form 
some  of  the  most  important  sources 
of  man's  food  supply.  Our  com- 
monest foods,  as  the  potato,  sweet 
potato,  carrot,  parsnip,  turnip,  and 
beet,  are  well-known  examples. 
Onions  contain  considerable  pro- 
teid  material.  The  sago  palm  is 
the  chief  support  of  many  of  the 
natives  of  Africa.  Each  adult 
tree  will  furnish  700  pounds  of 
sago  meal,  2^  pounds  being 
enough  to  support  a  man  one 
day.  The  cassava  root,  from  which 
tapioca  is  made,  is  one  of  the 
main  supports  of  African  natives. 
Sugar,  obtained  from  the  stem 
of  the  sugar  cane  and  from  the  beet  root,  is  a  world-known  commodity. 

The  following  table  shows  the  proportion  of  foods  in  some  of  the  com- 
moner roots  and  stems:  — 


1  2 

Stems  of  honey  locust  (i)  and  black  locust  (;2) ; 
Z/5,  leaf  scars;  the  thorns  (S)  on  the  honey 
locust  are  modified  stipules  (parts  of  leaves); 
the  thorns  ( T)  on  the  black  locust  are  modi- 
fied branches. 


Potato 75.0 

Carrot 89.0 

Parsnip ,     .  81.0 

Turnip 92.8 

Onion „     ,  91.0 

Sweet  Potato      ......  74.0 

Beet §2.2 


.OTEIDS 

Carbohydrai 

PE  Fats 

Ash 

1.2 

18.0 

0.3 

1.0 

0.5 

5.0 

0.2 

1.0 

1.2 

8.7 

1.5 

1.0 

0.5 

4.0 

0.1 

0.8 

1.5 

4.8 

0.2 

0.5 

1.5 

20.2 

0.1 

1.5 

Q.4 

13.4 

0.1 

0.9 

122  BOTANY 


Reference  Books 
for  the  pupil 

Andrews,  Botany,  All  the  Year  Round,  Chaps.  VI,  VII.     Araeii3an  Book  Company. 
Dana,  Plants  and  Their  Children,  pages  99-129.     American  Book  Company. 
Goff  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chaps.  IV,  V,  VI,  VIII,  XXI.     Ginn  and 

Company. 
Hunter  and  Valentine,  Laboratory  Manual  of  Biology.     Henry  Holt  and  Company. 
MacDougal,  The  Nature  and  Work  of  Plants.     The  Macmillan  Company. 


FOR   THE    TEACHER 

Apgar,  Trees  of  the  United  States,  Chaps.  II,  V,  VI.     American  Book  Company 

Goodale,  Physiological  Botany.     American  Book  Company. 

Gray,  Structural  Botany,  Chap.  V.     American  Book  Company. 

Leavitt,  Outlines  of  Botany.     American  Book  Company. 

Goebel,  Organography  of  Plants,  Part  V.     Clarendon  Press. 

Ganong,  The  Teaching  Botanist.     The  Macmillan  Company. 

Lubbock,  Buds  and  Stipxdes.     D.  Appleton  and  Company. 

Pinchot,  A  Primer  of  Forestry.     Bui.  No.  24,  Division  of  Forestry,  U.S.  Department 

of  Agriculture. 
Strasburger,  Noll,  Schenck,  and  Schimper,  A  Text-book  of  Botany.  .  The  Macmillan 

Compan5^ 
Ward,  The  Oak.     D.  Appleton  and  Company. 
Year  Book,  U.S.  Department  of  Agriculture,  1894,  1895,  1898. 


IX.     LEAVES    AND   THEIR  FUNCTIONS 


In  the  horse-chestnut  bud  previously  studied  the  brown  scales 
which  cover  the  green  scales  of  the  bud  can  be  shown  to  be  like 
in  structure  to  a  leaf  (homologous  to  a  leaf).  This  is  seen  better 
in  a  near  relative  of  the  horse-chestnut,  the  bucke3'e,  in  which  a 
series  of  changes  in  form  from 
brown  scales  to  green  leaves 
may  be  followed. 

Stipules.  —  The  bud  of  the 
tulip  tree  {Liriodendron  tulip- 
ifera)  is  an  admirable  source 
of  information  as  to  the  struc- 
ture of  a  leaf.^  In  the  buds  of 
a  tulip  tree,  however,  the  scales 
seem  to  act  as  wrappers  around 
the  little  leaves  and  not  to 
correspond  to  the  blade  of  the 
leaf,  but  to  an  outgrowth  of 
the  leafstalk  or  petiole  below 
it.  The  outgrowths  at  the 
base  of  a  leaf  are  known  as 
stipules.  The  scales  in  this  case  are  stipules  which  have  come  to 
protect  the  bud  at  a  time  when  the  delicate  parts  need  protec- 
tion most.  These  stipules  are  present  as  scales  in  many  other 
buds.  Frequently,  when  the  leaf  becomes  able  to  care  for  itself, 
the  stipules  fall  off  and  disappear.  Such  a  bud  is  the  elm,  as 
can  be  seen  by  a  careful  dissection.  Stipules  usually  are  paired. 
Notice  the  notched  appearance  of  the  scales  as  you  go  inward. 
Most  leaves  do  not  show  the  stipules  well,  although  a  complete 
leaf  is  supposed  to  be  supplied  with  them.  They  are  well  devel- 
oped in  the  rose  leaf. 

"  See  Hvinter  and  Valentine,  Manual,  page  37. 

123 


Palmately-veined  leaf  of  the  maple. 


124 


BOTANY 


Leaf  of  a  Dicotyledon.  —  If  we  now  take  up  the  study  of  a  simple 
leaf  such  as  the  elm,  we  find  that  the  parts  seen  in  buds  of  the 
tulip  tree  are  not  always  readily  found.     The  petiole  or  leafstalk 

runs  into  the  blade  of  the  leaf  as  the 
midrib.  Here  it  divides  to  form  the 
network  of  veins  found  in  the  leaves  of 
the  dicotyledonous  plants.^ 

Leaf  of  a  Monocotyledon.  —  In  the 
monocotyledons,  as  in  Tradescantia, 
or  in  the  leaves  of  a  grass,  there  is  no 
midrib,  the  leaf  being  traversed  by  a 
number  of  veins  which  run  lengthwise 
of  the  blade  and  give  it  the  name  of 
parallel-veined  leaf.^ 

Drawings  should  be  made  to  show  the 
parts  of  a  typical  simple  netted-veined  leaf 
and  that  of  a  leaf  parallel  veined.  Both 
drawings  should  be  natural  size  and  should 
have  all  parts  labeled. 


Parallel-veined  leaf  of  false 
Solomon  Seal. 


Modification  of  Blade.  —  The  blade  of  a  leaf  may  undergo  many 
modifications  in  different  species  of  plants.  It  may  have  almost 
any  shape,  from  a  thin  line  to 
an  almost  circular  outline. 
It  may  have  an  almost  smooth 
margin,  as  in  the  leaf  of  the 
rubber  plant  (Ficus  elastica), 
or  the  margin  may  be  more  or 
less  deeply  indented,  as  in 
the  tulip,  sassafras,  and  the 
oak. 

Compound  Leaf.  —  If  the 
margin  is  so  deeply  indented 
that  the  blade  is  cut  down  to 
the  midrib,  then  each  part  of 
the  blade  is  said  to  be  a  leaflet,  and  the  whole  leaf  is  compound. 
In  most  cases  it  is  easy  to  distinguish  a  compound  leaf:    (1)  by 

»  See  Hunter  and  Valentine,  Manual,  pages  39-^2.  2  /j^^.^  page  45= 


Pinnately-compound  leaf  of  rose,  showing 
stipules  {St.). 


LEAVES  AND  THEIR  FUNCTIONS 


125 


the  bud  in  the  axil  of  the  leaf,  that  is,  between  the  leafstalk 
and  the  branch;  (2)  by  the  presence  of  stipules  (this  is  well  seen 
in  the  rose  leaf) ;  (3)  by  the  fact  that  the  arrangement  of  veins  in 
the  leaflet  frequently  does  not  follow  the  same  system  of  branch- 
ing as  would  be  found  in  a  simple  leaf  of  the  same  form. 

Arrangement  of  Veins.  —  The  shape  of  the  blade  of  leaves  of 
dicotyledons  depends  somewhat  upon  the  arrangement  of  the 
veins.  If  the  blade  is  long  and  thin,  the  veins  will  be  found  to 
go  out  from  the  midrib  somewhat  like  the  side  parts  of  a 
feather;  hence  the  leaf  is  said  to  be 
feather  veined  (or  pinnate).  If  the  blade 
is  nearly  circular  in  outline,  the  veins 
will  leave  the  petiole  to  radiate  some- 
what like  fingers  from  the  jDalm  of  the 
hand.  Such  venation  is  said  to  be  pal- 
mate. 

The  same  general  arrangement  of  veins 
holds  true  for  compound  leaves.  The 
pea  and  locust  are  examples  of  pinnately 
compound  leaves,  the  horse-chestnut  of 
a  palmately  compound  leaf.^ 

Leaves  turn  toward  the  Light.  —  It  is 
a  matter  of  common  knowledge  that  green 
leaves  turn  toward  the  light.  Place 
growing  pea  seedlings,  oxalis,  or  any 
other  plants  of  rapid  growth  near  a  win- 
dow which  receives  full  sunlight.  Within 
a  short  time  the  leaves  are  found  to  be 
in  positions  to  receive  the  most  sunlight 
possible. 

Home  Experiment.  —  Turn  such  plants  after  two  or  three  days  so  that 
the  leaves  are  away  from  the  sun.  Make  observations  every  hour  during 
some  Saturday  morning  and  try  to  find  out  just  what  part  of  the  leaf  turns 
to  the  Kght. 

Effect  of  Light.  —  We  have  already  found  that  seedlings  grown 
in  total  darkness  are  almost  yellow-white  in  color,  that  the  leaves 

'  For  laboratory  work  on  leaves,  see  Hunter  and  Valentine,  Manual,  pages  39-47. 


The  skeleton  of  a  pinnately 
veined  leaf;  M.R.,  midrib; 
P.,  the  leafstalk  or  petiole; 
v.,  the  veins. 


126 


BOTANY 


A  lily,  showing  long,  narrow 
leaves. 


are  but  slightly  developed,  and  that  the  stem  has  developed  far 
more  than  the  leaves.     We  have  also  seen  (page  99)  that  a  green 

plant  will  grow  toward  the  source  of 
light,  even  against  great  odds.  This  effect 
of  light  is  seen  as  well  in  older  plants. 
Any  field  trip  will  reveal  the  fact  that 
in  low-lying  plants  the  leaves  which  are 
shaded  are  often  yellow  and  dwarfed. 
Plants  kept  in  poorly  lighted  rooms  at 
home  show  this. 

Arrangement  of  Leaves.  —  A  careful 
study  of  trees  in  any  park,  or  in  the 
woods,  shows  that  the  stems  of  trees  in 
thick  forests  are  usually  tall  and  straight 
and  that  the  leaves  come  out  in  clusters 
near  the  top  of  the  tree.  The  leaves 
lower  down  are  often  smaller  and  less 
numerous  than  those  near  the  top  of  the 
tree.  Careful  observation  of  any  plant 
growing  outdoors  shows  us  that  in  almost  every  case  the  leaves 
are  so  disposed  as  to  get  much  sunlight.  The  ivy  climbing  up  the 
wall,  the  morning  glory,  the 
dandelion,  and  the  burdock 
all  show  different  arrange- 
ments of  leaves,  each  pre- 
senting a  large  surface  to 
the  light.  Leaves  are  usu- 
ally definitely  arranged,  fit- 
ting in  between  each  other 
so  as  to  present  their  upper 
surface  to  the  sun.  Such  an 
arrangement  is  kno^vn  as  a 
leaf  mosaic.  Good  examples 
of  such  mosaics,  or  leaf  pat- 
terns, are  seen  in  the  alter- 
nate-leaved trees.  Here  the  leaves  turn,  by  the  twisting  of  the 
petioles,  so  that  all  the  leaves  present  their  upper  surface  to  the 


ihe  dandelion,  showing  a  whorled  arrangement 
of  long,  narrow  leaves. 


LEAVES  AND  THEIR  FUNCTIONS 


127 


3un.  In  the  case  of  the  dandelion  a  rosette  or  whorled  cluster  of 
leaves  is  found.  In  the  horse-chestnut,  where  the  leaves  come 
out  opposite  each  other,  the  older  leaves  have  longer  petioles  than 
the  young  ones.  In  the  mullein  the  entire  plant  forms  a  cone. 
The  old  leaves  near  the  bottom  have  long  petioles,  and  the  little 
ones  near  the  apex  come  out  close  to  the  main  stalk.  In  every 
case  each  leaf  receives  a  large  amount  of  light.     Other  modifica- 


Oxalis  plant  in  the  light. 


Oxalis  plant  after  two  hours  in  the 
dark. 


tions  of  these  forms  may  easily  be  found  on  any  field  trip.  See 
how  many  different  examples  of  leaf  mosaics  you  can  bring  in  to 
record  in  your  notebook. 

Effect  of  Absence  of  Light  upon  the  Leaves  of  the  Oxalis.^  —  Place  a  potted 
oxalis  in  a  dark  closet  or  box  for  two  or  three  hours,  having  previously 
exposed  it  to  direct  sunlight  for  a  short  time.  What  is  the  general  posi- 
tion of  the  leaves  after  removal  from  the  darkness?  Compare  with  the 
position  of  the  same  leaves  in  the  light. 

Sleep  Movements.  —  The  examination  of  a  number  of  young 
seedlings  of  buckwheat  or  sunflower  shows  that  after  a  few  hours 
in  darkness  the  leaves  droop.     The  leaves  of  the  bean  and  oxalis 

*  See  Hunter  and  Valentine,  Manual,  page  246. 


128 


BOTANY 


tend  to  droop  or  fold  after  a  much  shorter  exposure  to  the  dark 
ness.  These  changes  in  position  have  been  called  sleep  move- 
ments. Charles  Darwin  suggested  that  the  leaves  of  a  plant  which 
take  this  position  secure  protection  from  injury  by  frost.  In 
most  cases  the  movement  may  be  accounted  for  when  we  remem- 
ber that  leaf  blades  naturally  turn  their  upper  surfaces  toward  the 
light.  In  the  absence  of  light  the  leaf  blade  might  easily  be  in- 
fluenced to  droop  or  even  fold  by  the  counter  stimulus  of  gravity. 
Sensitiveness  to  Contact.  —  Leaves  of  some  plants  are  also  sensi- 
tive to  the  stimulus  of  contact.  The  sensitive  plant  (Mimosa 
pudica)  is  the  best-known  example.  Here  the  leaflets  of  the  com- 
pound leaf  respond  to  the  slightest  touch  by  folding  and  drooping. 
Under  normal  conditions  the  leaf  soon  returns  to  its  original  posi- 
tion. Changes  in  temperature  and  moisture  may  totally  prevent 
this  movement,  showing  that  the  living  matter  in  the  plant  is 

most  delicately  attuned  to  the 
influences  of  its  immediate 
surroundings. 

The  Sun  a  Source  of  En- 
ergy. —  We  all  know  the  sun 
is  a  source  of  most  of  the 
energy  that  is  released  on  this 
earth  in  the  form  of  heat  or 
light.  Solar  engines  have  not 
come  into  any  great  use  as 
yet  because  fuel  is  cheaper. 
Actual  experiments  have 
shown  that  vast  amounts  of 
energy  are  given  to  the  earth. 
When  the  sun  is  in  the  zenith, 
energy  equivalent  to  one  hun- 
dred horse  power  is  received 
by  a  plot  of  land  twenty-five  by  one  hundred,  the  size  of  a  city  lot. 
Plants  receive  and  use  much  of  this  energy  by  means  of  the  leaves. 

In  which  Part  of  a  Variegated  Leaf  does  Starch  Exist  P  —  Leave  two  plants, 
such  as  the  Coleus  (variety  with  red-colored  leaves)  or  Tradescantia  (the 
white-striped  leaf  variety)  and  another  Coleus  or  Tradescantia  with  the 


A  hydrangea  plant,  upon  the  leaves  of  which 
disks  of  cork  have  been  pinned  in  order  to 
exclude  sunlight  from  the  leaf. 


LEAVES   AND   THEIR  FUNCTIONS 


129 


leaves  entirely  green,  for  several  days  in  a  well-lighted  window  under  the 
same  conditions  of  light,  heat,  and  moisture.  After  two  days,  pick  several 
leaves  from  each  plant  and  place  them  in  separate  jars  in  wood  alcohol 
which  will  extract  the  leaf  green.  When  the  leaves  are  entirely  cohjrlcssi 
test  the  two  sets  of  leaves  witii  tincture  of  iodine.  Which  leaves  contain 
starch?  Which  parts  of  the 
leaf  contain  starch  ?  This  ex- 
periment shows  us  that  starch 
is  present  only  in  the  green 
part  of  the  leaf.^ 

Relation  of  Starch  Forma- 
tion to  Sunlight.  —  Another 
simple  experiment  will  give 
us  the  relation  of  the  presence 
of  starch  to  the  sunlight. 

Pin  or  sew  several  strips 
of  black  cloth,  such  as  alpaca, 
over  the  leaves  of  a  growing 
geranium.  Place  the  plant 
in  a  sunny  window  for  several 
days.  (This  can  be  reduced  to 
hours  if  the  plant  has  pre- 
viously been  kept  in  the  dark 
for  a  day  of  two.)    If  we  now 


Starchless  areas  in  leaves,  caused  by  excluding  sun- 
light with  strips  of  black  cloth. 


extract  the  leaf  green  as  before,  and  then  test  with  iodine,  we  find  that 
starch  is  present  only  in  that  part  of  the  leaf  which  was  exposed  to  the  sun. 
A  green  leaf,  when  attached  to  the  plant,  and  under  natural  conditions,  forms 
starch  in  the  sunlight.^ 

Examination  of  the  Under  Surface  of  a  Leaf  Under  the  Microscope.  —  Strip 
off  the  under  surface  of  a  leaf  of  Tradescantia,  stretch  it  flat  in  water  on  a 

glass  slide  and  examine  it  with  a  good  hand 
lens  (or,  better,  the  low  power  of  a  com- 
pound microscope);  numbers  of  little  oval 
structures  will  be  seen.  These  are  called 
stomata  (singular  stoma).  Notice  the  two 
cells,  usually  kidney-shaped,  one  on  each 
side  of  the  stoma.  These  are  the  guard  cells. 
By  change  in  shape  of  these  cells  the  open- 
ing of  the  stoma  is  made  larger  or  smaller. 
Note  also  the  larger  irregular  cells  of  the 
epidermis  or  outer  covering  of  the  leaf. 
About  what  is  the  ratio  of  the  number  of 
stomata  to  the  number  of  epidermal  cells  in 
a  small  part  of  the  leaf?  Draw  one  or  two 
stomata  showing  all  parts,  as  seen  under  a 
low  power  of  the  microscope.  If  we  now 
examine  a  very  thin  piece  of  a  leaf  cut  in 
cross  section,  we  can  make  out  the  rela- 
tion of  the  stomata  to  the  interior  of  the 
leaf. 

Lahoratorij  Exercise  on  Cross  Section  of  the  Leaf.  —  In  a  cross  section  of 
the  leaf  of  Tradescantia,  or  any  lily,  find  under  the  upper  epidermis 
a  layer  of  green  cells  closely  packed  together  (called  collectively  the 
palisade  layer).      These  cells  are  more  or  less  columnar  in  shape.     Under 

1  See  Hunter  and  Valentine,  Manual,  page  243.  2  jfji^.,  page  242. 

hunter's  BIOL.  —  9 


Surface  view  of  epidermis  of  lower 
surface  of  a  leaf;  e,  ordinary  epi- 
dermal cell;  g,  guard  cell. — 
Tschirch. 


130 


BOTANY 


these  are  several  rows  of  rather  loosely  placed  cells,  called  collectively  the 
spongy  parenchyma.     These  cells  do  not  contain  so  much  leaf  green  as 

those  of  the  palisade  layer.  Notice  the 
spaces  between  these  cells.  In  some  cases 
they  can  be  seen  to  communicate  with  the 
openings  of  the  stomata  in  the  lower  epi- 
dermis. Look  for  the  cut  ends  of  one  or 
more  of  the  fibro vascular  bundles  or  veins. 
The  cells  of  which  they  are  composed  are 
seen  to  be  greatly  thickened.^ 


Cross  Section  of  a  Green  Leaf.  — 
The  leaf  in  cross  section  shows  that  the 
whole  blade  is  a  series  of  tissues,  the  epi- 
dermis being  somewhat  thicker  walled  for 
protection,  the  under  surface  pierced  by 
numerous  pores.  Each  of  these  pores  con- 
nects with  an  air  space  which  penetrates 
more  or  less  the  whole  inside  of  the  leaf, 
but  especially  the  layer  just  outside  the 
lower  epidermis.  The  cells  of  the  palisade 
layer  we  shall  now  consider  more  in  detail. 


Section  of  a  leaf;  e,  epidermis; 
c,  cells  containing  chlorophyll 
granules;  p,  intercellular  pas- 
sages; g,  g,  guard  cells  of  stoma. 


Chloroplasts.  —  If  we  examine  some 
of  the  plant  cells  forming  part  of  the 
blade  of  the  leaf,  we  find  cells  which  are  almost  cylindrical  in 
form.  In  the  protoplasm  of  such  cells  are  found  a  number  of 
little  bodies  colored  green,  which  are  known  as  chloroplasts  or 
chlorophyll  bodies.  If  we  place  the  leaf  in  wood  alcohol,  we 
find  that  the  bodies  still  remain,  but  that  the  color  is  extracted, 
going  into  the  alcohol  and  giving  to  it  a  beautiful  green  color. 
The  chloroplasts  are,  indeed,  simply  part  of  the  protoplasm  of 
the  cell  stained  green.  If  the  plant  is  kept  in  the  sun,  the  chloro- 
plasts keep  their  green  color,  but  in  the  dark  this  color  is  gradually 
lost.  These  bodies  are  of  the  greatest  importance  directly  to 
plants  and  indirectly  to  animals.  The  chloroplasts,  by  means  of 
the  energy  received  from  the  sun,  manufacture  starch  out  of  certain 
materials.  These  materials  are  soil  water,  which  is  passed  up 
through  the  fibrovascular  bundles  into  the  veins  of  the  leaf  from 
the  roots,  and  carbon  dioxide,  which  is  taken  in  through  the  sto- 
mata or  pores,  with  which  the  under  surface  of  the  leaf  is  covered. 


*  For  detailed  laboratory  exercises,  see  Hunter  and  Valentine,  Maniml,  pages 
47-49. 


LEAVES  AND  THEIR  FUNCTIONS 


131 


Air  necessary  for  Starch  Formation.  —  The  following  experiment  shows 
not  only  that  sunlight  is  necessary  for  the  formation  of  starch,  but  also 
that  air  must  be  present. 

Experiment.  —  Select  any  small  plant  the  leaves  of  which  contain  stomata 
on  the  lower  surface  (rose  or  lilac).  Leave  the  plant  in  a  dark  room  for 
several  days,  so  that  the  starch  in  the  leaves  may  be  completely  used  up. 
Remove  the  plant  from  the  dark  room,  and  vaseline  the  lower  surface  of 
two  or  three  leaves,  marking  them  so  that  you  will  know  them.  After  a 
few  hours'  exposure  to  direct  sunlight,  pick  off  the  vaselined  Icax'cs  and  also 
some  others  from  the  same  plant.  Wash  them  in  wood  alcohol  and  then 
place  them  in  iodine.  What 
has  happened  in  the  case  of 
the  vaselined  leaves?  In  the 
case  of  the  other  leaves? 

Air  is  necessary  for  the 
process  of  starch  making 
in  a  leaf,  not  only  because 
carbon  dioxide  gas  is  ab- 
sorbed (there  are  from 
three  to  four  parts  in  ten 
thousand  present  in  the 
atmosphere),  but  also  be- 
cause the  protoplasm  of 
the  leaf  is  alive  and  must 
have  oxygen.  This  it  takes 
from  the  air  around  it. 
It  has  been  found  that 
plants  can  live  in  atmos- 


Diagram  to  Jllustrate  the  formation  of  starch. 


pheres  containing  as  much  as  10  per  cent  of  carbon  dioxide.  If 
more  than  10  per  cent  is  present,  they  may  die  of  suffocation, 
just  as  an  animal  would  die  if  placed  in  air  containing  a  large 
amount  of  carbon  dioxide. 

Comparison  of  Starch  Making  and  Milling.  —  The  manufacture 
of  starch  by  the  green  leaf  is  not  well  understood.  The  process 
has  been  compared  to  the  milling  of  grain.  In  this  case  the  mill 
is  the  green  part  of  the  leaf.  Jhe  sun  furnishes  the  motive  power, 
the  chloroplasts  are  the  millstones,  and  soil  water  and  carbon 
dioxide  are  the  raw  products  taken  into  the  mills.  The  manufac- 
tured product  is  starch,  and  a  certain  amount  of  waste  (rei)resented 
by  the  chaff  in  a  mill)  is  also  given  out.  This  waste  material  is  the 
element  oxygen. 


132 


BOTANY 


Oxygen  given  off  by  Green  Plants.  —  It  is  possible  to  prove  that 

oxygen  is  given  off  by  green  plants   in   sunlight.      The   common 

green  frog  scum  seen  in  shallow  ponds  is  often  so  full  of  bubbles 

that  it  is  buoyed  up  by  this  means  at  the  water's  surface.      If 

some  of  this  plant  or  other  green  water  weed  is  placed  in  a  large 

battery  jar  ^or  fruit  jar  in  a  sunny  window,  bubbles  of  gas  will 

be  seen  to  arise  from  it,  the  amount 

increasing  as  the  water  is  warmed  by 

the  sun's  rays. 

If  a  glass  funnel  is  placed  upside  down 
so  as  to  cover  the  plants,  and  then  a  test 
tube  full  of  water  Inverted  over  the  mouth 
of  the  funnel,  the  gas  may  be  collected  by 
displacement.  After  two  or  three  days  of 
hot  sun,  enough  of  the  gas  can  be  obtained 
to  make  the  oxygen  test.  Carefully  remove 
the  tube,  holding  the  thumb  over  the  end  of 
the  tube  to  prevent  the  escape  of  the  gas. 
A  glowing  match  end  thrust  into  the  tube 
will  burst  into  flame. 

Leaf  Structure  and  Functions.  —  To 

understand  the  process  fully  we  must 
refer  to  a  small  portion  of  the  leaf. 
Here  we  find  that  the  cells  of  the  green 
layer  of  the  leaf,  under  the  upper  epi- 
dermis, perform  most  of  the  w^ork. 
The  carbon  dioxide  is  taken  in  through 
the  stomata  and  reaches  the  green  cells 
by  way  of  the  intercellular  spaces  and 
by  diffusion  from  cell  to  cell.  Water 
reaches  the  green  cells  through  the 
tracheal  tubes  of  the  veins.  It  then 
passes  into  the  cells  by  osmosis  and  there  becomes  part  of  the  cell 
sap.  The  light  of  the  sun  easily  penetrates  to  the  cells  of  the 
palisade  layer,  giving  the  energy  needed  to  make  the  food.  This 
whole  process  is  a  very  delicate  one,  and  will  take  place  only 
when  external  conditions  are  favorable.  For  example,  too  much 
heat  or  too  little  heat  stops  starch  making ;  the  presence  of  stored 
food  in  the  leaf,  or  of  10  per  cent  of  carbon  dioxide  in  the  atmos- 
phere, may  stop  its  work. 


1 

■ 

Experiment  to  show  that  oxygen 
is  given  off  by  green  plants  in 
the  sunhght. 


LEAVES  AND  THEIR  FUNCTIONS 


133 


Photosynthesis.  —  The  process  by  which  starch  is  formed  in 
green  leaves  in  sunlight  is  called  photosynthesis.  This  process  is 
the  formation  of  carbohydrate  from  the  carbon  dioxide  absorbed 
from  the  air  and  from  the  water  present  in  the  cells  of  the  leaf. 

Chemical  Action  in  Starch  Making.  —  In  the  process  of  starch  making  in 
a  leaf,  water  (H2O)  and  carbon  dioxide  (CO2)  are  combined  in  such  a  way 
as  to  make  starch,  the  molecule  of  which  is  expressed  by  the  formula 
CeHioOs.  This  combination  is  expressed  as  follows :  5  HoO  +  6  CO2  = 
CeHioOs  +  120.  The  starch  thus  formed  is  either  stored  in  the  leaf  or 
changed  by  digestion  to  some  form  which  can  pass  by  osmosis  from  cell  to 
cell ;  that  is,  a  soluble  material  like  grape  sugar.  The  oxygen  is  passed  off 
through  the  stomata  of  the  leaf.^ 


Diagram  (after  Stevens)  to  illustrate  the  chemical  processes  which  take  place  in  the  cells  of 

a  green  leaf  in  the  sunlight, 

Proteid  Formation  in  the  Plant.  —  Proteid  material  is  a  food  which  is 
necessary  to  form  protoplasm.  Proteid  food  is  present  in  the  leaf,  and 
is  found  in  the  stem  and  root  as  well .  Proteids  can  seemingly  be  manufactured 
in  any  plant  cells,  irrespective  of  their  poi^ition  in  the  plant  body  The  pres- 
ence of  light  does  not  seem  to  be  a  necessary  factor.  The  mineials  brought 
up  in  the  soil  water  form  part  of  its  composition,  and  starch  or  grape  sugar 
give  three  elements.  The  element  nitrogen  is  taken  up  by  the  roots  as  a 
nitrate  (nitrogen  in  combination  with  lime  or  potash),  for  plants  are  unable 

^  It  seems  probable  that  food  material  is  first  made  in  the  form  of  a  mtgar,  then 
changed  to  starch ;  when  transported  from  one  part  of  the  plant  to  axiother  it  is 
changed  back  to  sugar. 


134 


BOTANY 


to  use  free  nitrogen  of  the  air  (ynth  the  exception  of  the  nitrogen-fixing  bac- 
teria). See  page  94.  Proteids  are  probably  not  made  directly  into  proto- 
plasm in  the  leaf,  but  are  stored  by  the  cells  of  the  plant  and  used  when 
needed,  either  to  form  new  cells  in  growth  or  to  repair  waste.  While  plants 
and  animals  get  their  food  in  different  ways,  they  make  it  into  living  sub- 
stance in  exactly  the  same  manner. 

Rapidity  of  Starch  Making.  —  Leaves  which  have  been  in  dark- 
ness soon  show  starch  to  be  present  when  exposed  to  Hght.    Squash 

leaves  make  three  fourths  of 
an  ounce  for  each  square  yard 
of  surface.  A  corn  plant  sends 
10  to  15  grams  of  reserve  ma- 
terial into  the  ears  in  a  single 
day.  The  formation  of  fruit, 
and  especially  the  growth  of  the 
grain  fields,  show  the  economic 
importance  of  this  fact.  Not 
only  do  plants  make  their  own 
food  and  store  it  away,  but 
they  make  food  for  animals  as 
well.  And  the  food  is  stored 
in  such  a  stable  form  that  it 
may  be  sent  to  all  parts  of  the 
world  in  the  form  of  grain  or 
other  fruits. 

Evaporation  of  Excess  Water. 
—  In  the  manufacture  of  starch 
and  proteid  an  enormous 
amount  of  water  is  taken  up 
by  the  roots  and  passed  to  the 
leaves  to  supply  the  needed 
amount  of  mineral  matter. 
The  excess  of  water,  which  often  amounts  in  a  single  day  to  more 
than  the  entire  weight  of  the  plant,  is  evaporated  (passed  off  as 
vapor)  through  the  stomata.  That  water  is  passed  through  the 
blade  of  the  leaf  in  the  form  of  moisture  is  shown  by  the  follow- 
ing experiment :  — 


Experiment  to  show  transpiration.  Notice 
that  roots  covered  with  root  hairs  have 
grown  out  of  the  main  stem  of  the  plant  In 
response  to  the  moist  condition  existing 
outside  of  the  riibber-covered  flower-pot 
and  within  the  bell  jar. 


LEAVES   AND   THEIR  FUNCTIONS 


135 


Pass  the  petiole  of  a  green  leaf  through  a  cardboard  cover  into  a  glass  of 
water.  Seal  the  space  between  the  petiole  and  cardboard  with  grafting 
wax  (chewing  gum  will  do).  Invert  another  glass  over  the  first.  After  an 
hour,  examine  the  upper  glass  and  notice  where  the  moisture  has  collected. 
How  did  it  get  there? 

The  following  experiment  shows  that  the  amount  of  water  passed  off 
through  the  leaves  by  the  process  called  transpiration  is  great  enough  to  be 
measured.  Cover  with  a  rubber  cloth  a  flowerpot  in  which  a  vigorous  plant 
is  growing,  so  that  only  the  stem  and  leaves  are  outside  of  the  rubber  cover. 
Before  fastening  the  cloth,  water  the  plant  well.  Now  place  the  flower  pot 
upon  a  pan  of  a  balance  and  put  weights  in  the  other  pan  until  the  pans 
balance.  Leave  the  plant  in  a  sunny  window  for  several  hours,  and  after  a 
given  time  note  the  position  of-  the  pans.  Measure  the  amount  of  water 
lost  by  removing  weights  till  the  pans  balance  again. 

Amount  of  Water  Lost  by  Transpiration.  —  A  relatively  large 
amount  of  water  passes  off  by  transpiration  every  twenty-four 
hours.  A  small  grass  plant  on  a  summer's  day  evaporates  more 
than  its  own  weight  in  water.  This  would  make  nearly  half 
a  ton  of  water  distributed  to  the  air  during  twenty-four  hours 
by  a  grass  plot,  twenty-five  by  one  hundred  feet,  the  size  of  the 
average  city  lot.  According  to  Ward,  an  oak  tree  may  pass  off 
two  hundred  and  twenty-six  times  its  own  weight  in  water  during 
the  season  from  June  to  October. 

From  which  Surface  of  the  Leaf  is  Water  Lost  ?  —  In  order  to 
find  out  whether  water  is  passed  out  from  any  particular  part  of 


Experiment  to  show  through  which  surface  of  a  leaf  water  passes  off. 


136 


BOTANY 


the  leaf,  we  may  remove  two  leaves  of  the  same  size  and  weight 
from  some  large-leaved  plant  —  a  mullein  was  used  for  the  illustra- 
tions given  —  and  cover  the  upper  surface  of  one  leaf  and  the 
lower  surface  of  the  other  with  vaseline.  The  petioles  of  each 
should  be  covered  with  wax  or  vaseline,  and  the  two  leaves  exactly 
balanced  on  the  pans  of  a  balance  which  has  previously  been  placed 
in  a  warm  and  sunny  place.  Within  an  hour  the  leaf  which  has 
the  upper  surface  covered  with  vaseline  will  show  a  loss  of  weight. 
Examination  of  the  surface  of  a  mullein  leaf  shows  us  that  the  lower 
surface  of  the  leaf  is  provided  with  stomata.  It  is  through  these 
organs,  then,  that  water  is  passed  out  from  the  tissues  of  the  leaf. 
Regulation  of  Transpiration.  —  The  stomata  of  leaves  close  at 
night.     On  days  when  there  is  little  humidity  they  tend  to  close, 

but  when  the  water  supply  is  abun- 
dant they  open.  This  automatic 
regulation  is  of  very  great  impor- 
tance to  the  life  of  the  plant,  since 
evaporation  of  water  is  thus 
limited,  and  consequent  wilting 
of  the  leaves  prevented. 

The  change  in  the  size  of  the  open- 
ing of  the  stomata  appears  to  be  due 
to  the  fact  that  the  protoplasm  of  the 
guard  cell  takes  up  and  loses  fluids 
rather  easily.  This  process  we  have 
already  noticed  under  the  name  of 
turgor.  With  an  increase  in  the  tur- 
gidity  of  the  guard  cells,  which  results 
after  an  osmotic  inflow  from  surround- 
ing cells  of  the  leaf,  the  guard  cells 
change  shape  so  as  to  increase  the  size 
of  the  opening  between  them.  Simi- 
fluids  from  the  guard  cells,  the  opening 


Diagrams  of  a  stoma;  a,  surface  view  of 
an  opened  stoma;  b,  same  stoma 
closed  (after  Hansen);  c,  diagram  of  a 
transverse  section  through  a  stoma  — 
dotted  Hnes  indicate  the  closed  position 
of  the  guard  cells,  the  heavy  lines  the 
open  condition.    (After  Schwendener.) 

larly,  with  a  loss  of  water  or  other 
becomes  smaller. 


The  Effect  of  Transpiration  on  Water  within  the  Stem.  —  It  has 
already  been  noted  that  root  pressure  alone  will  not  account  for 
the  rise  of  water  to  the  tops  of  very  tall  trees.  The  following 
experiment  shows  that  transpiration  exerts  a  lifting  power  upon 
the  fluids  within  the  stem: — - 


LEAVES   AND   THEIR  FUNCTIONS 


137 


~^P^ 


Into  one  end  of  a  glass  tube  fit  a  rubber  stopper  with  a  hole  through  it 
Into  this  hole  insert  the  stem  (freshly  cut  off  under  water)  of  a  leafy  branch 
from  an  actively  growing  tree.     Seal  the  stem* in  with  melted  wax.     Fill 
the  tube  with  cool,  boiled  water,  and  immerse  the 
open  end  in  mercury  as  shown  in  the  figure. 

Respiration  by  Leaves.  —  All  living  things, 

with  the  possible  exception  of  some  bacteria, 

require  oxygen  in  order  to  live.     It  is  by 

means  of  the  oxidation  of   food   materials 

within  the  plant's  body  that  the  energy  used 

in  growth   and  movement   is   released.     A 

plant  takes  in  oxygen  largely  through  the 

stomata   of   the   leaves,    to   a   less    extent 

through  the  lenticels  in  the  stem,  and  through 

the  roots.    In  young  plants,  especially,  much 

oxygen  is  taken    up    by  the    latter-named 

organs.     Thus  the  rapidly  growing  tissues 

receive  the  oxygen  necessary  for  them  to 

perform   their   work.     It  can  be  shown  by 

experiment  that  a  plant   uses    up    oxygen 

in  the  darkness ;  in  the  light  the  amount  of 

oxygen  given  off  as  a  by-product  in  the  process  of  starch  making 

is,  of  course,  much  greater  than  the  amount  used  by  the  plant. 
Summary.  —  From   the   above   paragraphs   it   is   seen   that   a 

leaf  performs  the  following  functions:    (1)  breathing,  (2)  starch 

making,  with  the  inci- 
dental passing  out  of 
oxygen,  (3)  formation  of 
proteids,  with  their  diges- 
tion and  assimilation  to 
form  new  tissues,  and 
(4)  the  transpiration  of 
water. 

Modified  Leaves.'^  Leaves 
as  Spines.  —  Examine  a  holly 
leaf.     Of  what  use  might  the 


Apparatus  to  show  the  up- 
ward pull  of  leaves. 
(After  Detmer.) 


Modified  leaves  (holly).    Note  the  spines. 


stiffened  spines  be  to  the  plant?     To  what  dangers  might  such  a  leaf  be  ex- 
posed?    Remember  that  holly  keeps  green  in  a  much  colder  atmosphere 

1  For  exercises  on  modified  leases,  see  Hunter  and  Valentine,  Manual,  pages 
40,  41,  42,  45,  46. 


138 


BOTANY 


than  many  other  plants.     Compare  the  spines  of  the  honey  locust,  black 
locust,  and  barberry.    Look  for  leaf  traces  and  buds  on  the  stem,  and  decide 

from  the  relative  position  of  the  thorns  and 
these  structures  which  of  the  above-named 
structures  are  modified  leaves.  (Sometimes 
a  spine  may  be  part  of  a  leaf,  as  the  stipule.) 
Cactus.  —  In  the  prickly  pear  cactus, 
notice  that  above  the  spines  are  little  buds. 
The  position  of  the  bud  shows  the  spine  to 
be  a  modified  leaf.  What  reason  can  you 
give  for  this  modification  of  the  leaf  of  the 
cactus  ?  How  is  the  plant  body  modified  to 
meet  the  conditions  of  life  in  a  desert? 
Note  the  thickened  stem. 

If  a  cactus  is  cut  open,  it  will  be  found 
to  contain  a  very  considerable  amount  of 
water.  The  Indians  of  the  New  Mexican 
desert  region,  when  far  from  a  source  of 
water,  sometimes  cut  off  the  top  of  a  large 
cactus,  mash  up  the  soft  interior  of  the 
thickened  stem,  squeeze  out  the  pulp,  and 
thus  obtain  several  quarts  of  drinkable 
water. 

Protection  by  Hairs.  —  In  the  mul- 
lein, one  of  our  hardiest  weeds,  the  leaf  is 
covered  with  a  coating  of  finely  branched 
hairs.  Might  such  a  covering  be  of  use  to 
the  leaf?     In  what  ways? 

Leaves  modified  for  Use  in  Climbing. 
—  Sometimes,  as  in  the  leaf  of  the  pea,  a 
part  of  the  leaf  is  modified  for  the  purpose  of  climbing.  In  this  case 
a  part  of  the  leaf,  called  the  tendril,  becomes  especially  sensitive  to  the 
stimulus  of  touch,  and  upon  touching  an  object  coils  around  it.  Almost 
any  part  of  the  leaf,  or  indeed  the  entire  leaf,  may  be  modified  to  become  a 
tendril.  What  part  of  the  leaf  of  the  pea  here  forms  the  tendril?  If 
material  can  be  obtained,  work  out  the  morphology  of  modified  parts  of  the 
clematis;   wild  grape;   Virginia  creeper. 

Storage  of  Food  or  Water  in  Leaves.  —  Leaves  may  be  modified  for 
the  storage  of  food  or  water.  Test  an  onion,  which  is  a  collection  of  thickened 
leaves  closely  wrapped  to  form  what  is  called  a  bulb,  for  starch,  sugar,  and 
proteid.  Squeeze  the  leaves  of  the  Sedum  and  notice  the  water  contained 
in  them.  The  Agave  is  a  desert  plant  in  which  the  leaves  have  become 
greatly  thickened  as  a  water  and  food  storage.  Make  a  list  of  any  plants 
you  know,  as  the  cabbage,  that  store  food  in  the  leaves. 

Reduced  Leaves.  —  Leaves  may  be  reduced  to  scales  or  lost  altogether. 
In  the  asparagus  what  seem  to  be  tiny  leaves  are  branches  which  spring 


A  cactus,  showing  the  leaves  modi 
fied  into  spines. 


LEAVES  AND  THEIR  FUNCTIONS 


139 


from  the  axils  of  the  true,  very  tiny,  scalelike  leaves.    The  spines  noted  in  the 
cactus  are  examples  of  reduced  leaves. 

Leaves  as  Insect  Traps.  —  Most  curious  of  all  are  the  modifications  of  the 
leaf  into  insect  traps.  It  frequently  happens  that  the  habitat  of  a  plant  will 
not  furnish  the  raw  food  materials  necessary  to  form  proteid  food  and  to 
build  protoplasm.  Nitrogen  is  the  lacking  element.  The  plant  has  become 
adapted  to  these  conditions  and  obtains  nitrogenous  food  from  the  bodies  of 
insects  which  it  catches.  Examples  of  insect  traps  are  the  common  bladder- 
wort  (Utricularia) ,  the  Venus's  flytrap  (Dioncea  muscipula),  the  sundew 
(Drosera  rotundifolia) ,  and  certain  of  the  pitcher  plants. 


Bladderwort,  showing  finely  dissected  submerged  leaves  bearing  blades  which  capture 

animalcula. 

Bladderwort. — The  simplest  contrivance  for  the  taking  of  animal  food 
by  the  leaf  is  seen  in  the  bladderwort.  Here  certain  of  the  leaves  are  modi- 
fied into  little  bladders  provided  with  trapdoors  w^hich  open  inwards.  Small 
water-swimming  crustaceans  (as  water  fleas,  etc.)  push  their  way  into  the 
trap  and  there  die,  perhaps  of  starvation.  Bacteria,  causing  decay,  soon 
break  down  their  bodies  into  soluble  substances,  the  nitrogenous  portion  of 
which  is  absorbed  by  the  inner  surface  of  the  bladders  and  used  by  the  plant 
as  food. 

Venus's  Flytrap.  —  In  the  Venus's  Kytrap,  a  curious  plant  found  in  our 
Southern  states,  the  apex  of  the  leaf  is  peculiarly  modified  to  form  an  insect 


140 


BOTANY 


Leaf  of  sundew  closing 
over  captured  insect. 


trap.     Each  margin  cf  the  leaf  is  provided  with  a  row 

of  hairs;    there  are  also  three  central  hairs  on  each 

side  of   the   midrib.     The   hairs   are    sensitive  to   a 

stimulus  from  without.     The  blade  is  so  constructed 

that  the  slightest  stimulus  causes  a   closing  of  the 

leaf   along  the   midrib.     The  surface   of  the  leaf  is 

provided  with  many  tiny  glands,   which  pour  out  a 

fluid  capable  of  digesting  proteid  food.     Thus  an  in- 
sect, caught  between  the  halves  of  che  leaf  blade,  is 

held  there  and  slowly  digested. 

Sundew.  —  In  the  sundew  the  leaves  are  covered 

with  long  glandular  hairs,  each  of  which  is  extremely 

sensitive  to  the  stimulus  of  any  nitrogenous  substance. 

These  hairs  exude  a  clear,  sticky  fluid  which  first  ren- 
ders more  difficult  the  escape  of  the  insect  caught  in 

the  hairs,  and  then  digests 
the  nitrogenous  parts  of  the 
insect  thus  caught.  Charles 
Darwin,  in  a  series  of  experi- 
ments, found  that  these  hairs 
do  not  respond  to  the  stimu- 
lus of  falling  raindrops,  but 
that  a  bit  of  hair  weighing 
only  y  8  y  JO-  of  a  grain  is  enough 
to  cause  the  slight  bending  of 
the  hairs. 

Pitcher  Plants.  —  The 
common  pitcher  plant  has  an 
urn-shaped  leaf  which  is  modi- 
fied to  hold  water.  Many 
small  flies  and  other  insects 
find  their  way  into  the  pitcher 
and  are  eventually  drowned 
in  the  cup.  Whether  the  plant 
actually  makes  use  of  the  food 
thus  obtained  is  a  matter  un- 
settled. In  a  tropical  form, 
called  Nepenthes,  the  petiole 
of  the  leaf  forms  the  pitcher, 
the  blade  of  the  leaf  forming 
a  kmd  of  lid.  In  the  fuU- 
grcwn  plants  this  lid  stands 

Pitcher  plant;  a,  leaf;  6,  cross  section;  c,  longitudinal        open,    perhaps   as    an   attrac- 
section.    Note  the  insects  at  the  bottom,  and  the        -•       j.     •  x        tt  i        ^ 

inward-pointing  hairs  at  the  top.  tion  to  msects.    Honey  glands 


LEAVES   AND   THEIR  FUNCTIONS  141 

on  the  pitcher  lead  the  insect  to  its  destruction.    The  insect  slips  into  the 
fluid  in  the  pitcher,  is  digested,  and  the  proteid  portion  absorbed. 

Leaves  as  Food.  —  Some  leaves  are  used  directly  by  man  for 
food.  Examples  are  cabbage,  lettuce,  Swiss  chard,  kale,  broccoli, 
and  many  others.  These  leaves  contain  (with  a  large  percentage 
of  water)  gluten  (a  proteid),  starch,  oil,  and  mineral  matter. 
These  foods,  properly  admixed  with  certain  fleshy  foods,  are  of 
great  importance  in  giving  a  balance  to  diet. 

Economic  Use  of  Leaves.  —  The  practical  use  of  green  plants 
to  man  is  very  great.  Plants  give  off  oxygen  in  the  sunlight  and 
use  carbon  dioxide,  which  is  given  off  by  animals  in  the  breath. 
Thus  parks  containing  green  trees  are  truly  the  breathing  places 
of  the  city. 

Another  very  important  use  to  man  is  seen  in  the  fact  that 
leaves,  falling  to  the  ground,  help  to  form  a  rich  covering  of 
humus,  which  acts  as  a  coat  to  hold  in  moisture.  The  forests  are 
our  greatest  source  of  water  supply.  The  cutting  away  of  the 
forest  always  means  a  depletion  of  the  reserv^e  water  stored  in 
soil;  with  consequent  floods  and  droughts  in  alternation. 


Reference   Books 
for  the  pupil 


Andrews,  Botany  All  the  Year  Round,  pages  46-62.     American  Book  Company. 

Leavitt,  Outlines  of  Botany.     American  Book  Compan3\ 

Dana,  Plants  and  their  Children,  pages  135-185.     American  Book  Company. 


FOR    THE    TEACHER 

Gray,  Structural  Botany,  pages  85-131.     American  Book  Company. 

Goodale,  Physiological  Botany,  pages  337-353  and  409-424.  American  Book  Com- 
pany. 

Darwin,  Insectivorous  Plants.     D.  Appleton  and  Company. 

Green.      Vegetable  Physiology.     J.  and  A.  Churchill. 

Lubbock,  Flowers,  Fruits,  and  Leaves,  Last  Part.     The  Macmillan  Company. 

MacDougal,  Practical  Text-hook  of  Plant  Physiology.  Longmans,  Green,  and  Com- 
pany. 

Report  of  the  Division  of  Forestry,  U.S.  Department  of  Agriculture,  1899. 

Strasburger,  Noll,  Schenck,  and  Schimper.  A  Text-hook  of  Botany.  The  Mac- 
millan Company. 


X.    ECOLOGY 


Simplest  Plant  Body  a  Thallus.  —  It  has  been  found  by  botanists 
that  the  plants  which  are  the  simplest  in  body  structure  are  those 
which  live  in  the  water.  Sometimes  such  simple  plants  are  found 
upon  rocks  or  on  the  bark  of  trees.  In  such  plants  we  can  dis- 
tinguish no  root,  stem,  or  leaf. 


^^  The  plant  body  may  even  be 

^^^^  ^1^  spherical  in  outline  and  con- 

^^^^L^  ^^P!^k        ®^^^  ^^  ^^^'  ^  s^^g^^  ^^^^-     Such 

^^^mb||^J|^  '      ^B^^^       ^^6  the  plants  which  give  the 
^^^^9^9  fi^^^^^^         green    color  often   found   on 
^^^JUTJ^^^  >^be  bark  of  trees.    Still  other 

•^^jnP^B^  plants   are  threadlike  in  ap- 

pearance.     Others,     as    sea- 

A  red  seaweed,  an  example  of  a  thallus  body.  i       i_  -i  i  t_  i 

weeds,  have  a  ribbon-shaped 
body.  All  of  these  diverse  shapes  of  plant  bod}^  are  grouped 
under  the  general  name  of  thallus.  The  simjplest  jorms  of  plants 
have  a  thaUuslike  body. 

Adaptation  to  Environment.  —  This  kind  of  body  is  of  use  to 
a  plant  which  lives  in  the  water  as  a  root  to  take  in  water.  Plants, 
as  well  as  animals,  are  greatly  affected  by  what  immediately  sur- 
rounds them,  their  environment.  It  is  believed  (and  we  have 
shown  in  our  experiments)  that  the  environment  (conditions  of 
temperature,  moisture,  soil,  etc.)  is  capable  of  changing  or  modify- 
ing the  structure  of  plants  very  greatly.  The  change  ivhich  a 
plant  or  animal  has  undergone,  that  fits  it  for  conditions  in  which  it 
lives,  is  called  adaptation  to  environment. 

The  factors  which  act  on  plants  and  which  make  up  their  environ- 
ment are  soil,  water,  temperature,  and  light. 

The  first  plants  were  probably  water-loving  forms.  It  seems 
likely  that,  as  more  land  appeared  on  the  earth's  surface,  plants 
became  adapted-  to  changed    conditions   of    life    on    dry   land, 

142 


ECOLOGY  143 

With  this  change  in  habit  came  a  need  of  taking  in  water,  of 
storing  it,  of  conducting  it  to  various  parts  of  the  organism.  So 
it  does  not  seem  unlikely  that  plants  came  to  have  roots, 
stems,  and  leaves  and  thus  adapted  to  their  environment  on 
dry  land.  We  find  in  nature  that  those  plants  or  animals  which 
are  best  adapted  or  fitted  to  live  under  certain  conditions  are 
the  ones  which  sur\dve  or  drive  other  competitors  out  from 
their  immediate  neighborhood.  Nature  selected  those  which 
were  best  fitted  to  live  on  dry  land,  and  those  plants  eventually 
covered  the  earth  with  their  progeny. 

As  we  have  found  in  our  experiments,  young  plants,  and  indeed 
any  living  plants,  are  delicate  organisms,  which  are  affected  pro- 
foundly by  the  action  of  forces  outside  themselves.  It  is  impossi- 
ble not  to  see  this  after  we  have  grown  seedlings  with  and  with- 
out light,  with  much  water  and  with  little  water.  Pea  seedlings 
may  grow  for  a  time  in  sawdust,  but  we  know  that  they  will  be 
much  healthier  and  will  live  longer  if  allowed  to  germinate  in 
soil  under  natural  conditions. 

Desert  Conditions.  —  If  we  examine  plants  growing  in  a  dry 
climate,  as  cactus,  sage  brush,  aloe,  etc.,  we  find  that  the  leaf 
surface  is  invariably  reduced.  Leaves  are  reduced  to  spines  in 
the  cactus.  Some  plants,  such  as  the  three-angled  spurge,  which 
bear  leaves  in  a  condition  of  moderate  water  supply,  take  on 
the  appearance  of  a  cactus  under  desert,  conditions.  Thus  they 
lose  their  evaporating  leaf  surface  by  having  the  leaves  changed 
into  spines. 

This  adaptation  is  evidently,  if  our  experiments  count  for 
anything,  the  result  of  the  action  of  forces  outside  the  plants; 
that  is,  it  is  an  adaptation  to  environment. 

Water  Supply.  —  Water  supply  is  one  of  the  important  factors 
in  causing  changes  in  structure  of  plants.  Plants  which  live  en- 
tirely in  the  water,  as  do  many  of  the  plants  known  as  algse,  have 
slender  parts,  stemlike,  and  yet  ser^nng  the  place  of  a  leaf.  The 
interior  of  such  a  plant  is  made  up  of  spongy  tissues  which  allow 
the  air,  dissolved  in  the  water  in  which  they  live,  to  reach  them. 
If  leaves  are  present,  as  m  the  pond  lily,  the  stomata  are  alJ  in 
the  upper  side  of  the  leai: 


144 


BOTANY 


Plants  living  in  water  have  loose  and 
spongy  tissues ;  many  large  intercellu- 
lar spaces  are  found  in  stems  or  leaves. 
In  one  pond  lily  (Nelumbo  lutea)  these 
spaces  in  the  leaf  communicate  with 
large  spaces  in  the  veins  of  the  leaf,  and 
these  in  turn  with  spaces  in  the  petiole, 
stem,  and  root,  so  that  all  parts  of  the 
plants  are  in  communication  with  the 
air  above.  The  roots  of  a  plant  living 
wholly  in  water  are  not  needed  for  sup- 
port, hence  they  arc  often  short  and 
stumpy.  They  do  not  need  to  be 
modified  to  absorb  water ;  consequently 
the  absorbing  surface  lacks  root  hairs. 
The  whole  plant,  when  under  water,  is 
usually  modified  to  take  water  (and 
with  it  food)  from  its  immediate  en- 
vironment. 

Hydrophytes.  —  If  water  is  pres- 
ent in  such  quantity  as  to  satu- 
rate the  soil  in  which  the  plant 
lives  the  conditions  of  its  en- 
vironment are  said  to  be  hydrophytic  and  such  plant  is  said  to 
be  a  hydrophyte. 

Xerophytes.  —  The  opposite 
of  hydrophytic  conditions  is 
seen  when  the  soil  is  very  dry. 
Such  a  condition  is  known  as 
xerophytic,  and  the  plants  liv- 
ing in  these  conditions  are 
xerophytes.  Such  is  the  con- 
dition in  a  desert.  We  have 
seen  that  the  most  important 
adaptations  of  xerophytes  are 
such  as  prevent  evaporation 
of  water  from  their  bodies. 
The  leaf  surface  is  reduced, 
the  leaves  being  changed  into 
spines  as  in  the  cactus,  or  very 
greatly  reduced  in  size,  as  in 
the  switch  plants  of  our  alkali 


A  water  plant,  showing  the  finely  divided 
leaflike  pax'ts. 


Plants  with  floating  leaves. 


ECOLOGY 


145 


deserts.  The  stem  may  be  thickened  and  full  of  water;  a  covering  of  hairs 
or  some  other  covering  may  occur  and  lessen  loss  of  moisture  by  evapora- 
tion.    Examples  of  xerophytes  are  the  cacti,  yuccas,  agaves,  etc. 


^'sa^^f^''' 


:^S£Sft*Sfe*h: 


-*3^-^=f?c?^>-^ 


,^&^_   •«. 


m. 


•3k 


,1L  ■  .-Jys. 


Xerophytic  conditions.    A  typical  desert. 

Halophytes.  —  If  the  water  or  saturated  soil  in  which  the  plant 
lives  contains  salts,  such  as  sea  salt  or  the  al|<:ali  salts  of  some  of 
our  Western  lakes,  then  the  conditions  are  said  to  be  halopJiytic, 
and  a  plant  living  under  such  conditions  is  known  as  a  halophyte. 

Halophytes  show  many  characteristics  which  xerophytes  show, 
spines  or  hairs,  thick  epidermis,  fleshy  leaves,  all  being  characters 
which  show  that  the  water  supply  of  the  plant  is  limited.  The 
density  of  the  salt  water  in  the  soil  makes  it  difficult  for  the 
plant  to  absorb  water;  hence  these  characters  are  developed. 

Mesophytes.  —  Most  plants  in  the  Temperate  Zone  occupy  a 
place  midway  between  the  xerophytes  on  one  hand  and  hydro- 
phytes on  the  other.  They  are  plants  which  require  a  moderate 
amount  of  water  in  the  soil  and  air  surrounding  them.  Such  are 
most  of  our  forest  and  fruit  trees,  and  many  of  our  garden  vege- 
tables. Conditions  of  moderate  moisture  are  called  mesopJujtic ; 
the  plants  living  thus  are  known  as  mesophytes. 

It  may  easily  be  seen  that  plants  which  are  mesophytes  at  one 
time  may  under  some  conditions  of  weather  be  forced  to  undergo 
xerophytic  or  hydrophytic  conditions.  An  oak  tree  may  receive 
no  water  through  the  roots  during  the  winter  because  the  surface 

hunter's   BIOL. —  10 


146 


BOTANY 


A  mesophytic  condition.    A  valley  in  central  New  York. 

of  the  ground  is  frozen,  thus  preventing  water  from  finding  its 
way  below  the  surface. 

Plant  Societies.  Field  Work.  —  Any  boy  or  girl  who  has  access  to  a 
vacant  lot  or  city  park  can  easily  see  that  plants  group  themselves  into 
societies.  Certain  plants  live  together  because  they  are  adapted  to  meet 
certain  conditions.  Societies  of  plants  exist  along  the  dusty  edge  of  the 
roadside,  under  the  trees  of  the  forest,  along  the  edge  of  the  brook,  in  a 
swamp  or  a  pond.  It  should  be  the  aim  of  the  field  trips  to  learn  the  names 
of  plants  which  thus  associate  themselves  and  the  conditions  under  which 
they  Uve,  and  especially  their  adaptations  to  the  given  conditions.^ 

Other  Factors. — It  is  a  matter  of  common  knowledge  that  plants  in 
different  regions  of  the  earth  differ  greatly  from  one  another  in  shape,  size, 
and  general  appearance.  If  we  study  the  causes  for  these  changes,  it  be- 
comes evident  that  the  very  same  factors  which  govern  hydrophytic,  xero- 
phytic,  and  mesophytic  conditions  determine,  at  least  in  part,  the  habits  of 
the  plants  growing  in  a  given  region  —  be  it  in  the  tropics  or  arctic  regions. 
But  in  addition  to  water  supply  the  factors  of  temperature,  light,  soil,  wind, 
etc.,  all  play  important  parts  in  determining  the  form  and  structure  of  a  plant. 

^  Suggestions  for  such  excvirsions  are  found  in  Andrews,  Botany  all  the  Year 
Round,  Lloyd  and  Bigelow,  The  Teaching  of  Biology,  Ganong,  The  Teaching  Botanist, 
and  many  other  books.  A  convenient  form  of  excursion  is  found  in  Himter  and 
Valentine,  Manual,  page  202. 


ECOLOGY 


147 


Desert  Conditions.  —  In 
the  deserts  of  Central  Africa 
and  those  of  the  Western 
United  States  the  conditions 
of  temperature,  and  especially 
lack  of  moisture,  are  essen- 
tially the  same.  We  find  in 
both  regions  plants  the  leaves 
of  which  are  either  very  small 
or  entirely  lacking,  their  place 
having  been  taken  by  spines 
or  thorns.  In  some  plants, 
Agave,  for  example,  leaves  are 
present,  but  "are  thick  and 
fleshy  to  hold  water. 

Cold  Regions.  —  Here 
plants,  which  in  lowland  re- 
gions of  greater  warmth  and 
moisture  have  a  tall  form  and 
luxuriant  foliage,  are  stunted 
and  dwarfed;  the  leaves  are 
smaller  and  tend  to  gather 
in  rosettes  or  are  otherwise 
closely  placed  for  warmth  and 
protection.  As  we  climb  a 
mountain  we  find  the  average 


Two  plant  societies:  in  the  foreground  plants  living 
in  conditions  of  much  moisture;  in  the  back- 
ground true  mesophytes,  a  tree  society. 


Polar  limit  of  trees,  northern  Russia. 


148 


BOTANY 


size  of  plants  decreases  as  we  approach  the  line  of  perpetual  snow.  The 
largest  trees  occur  at  the  base  of  the  mountains;  the  same  species  of  trees  near 
the  summit  appear  as  mere  shrubs.  Continued  cold  and  high  winds  are  evi- 
dently the  factors  which  most  influence  the  slow  growth  and  the  size  and 
shape  of  plants  near  the  mountain  tops.  Cold,  Httle  light  during  the  short 
days  of  the  long  winter,  and  a  slight  amount  of  moisture  all  act  upon  the 
vegetation  of  the  arctic  region,  tending  toward  very  slow  growth  and  dwarfed 
and  stunted  form.  Trees  over  five  hundred  years  old  have  been  noted  in 
cold  regions  with  trunks  less  than  three  feet  in  diameter  at  the  base. 


Conditions  in  a  moist,  semi-tropical  forest.    The  so-called  "  Florida  moss  "  is  a  flowering 
plant.    Notice  the  resurrection  ferns  on  the  tree  trunk. 

Vegetation  of  the  Tropics.  —  A  rank  and  luxuriant  growth  is  found  in 
tropical  countries  with  a  uniformly  high  temperature  and  large  rainfall.  In 
general  it  may  be  estimated  that  the  rainfall  in  such  countries  is  at  least 
twice  as  great  as  that  of  New  York  state,  and  in  many  cases  three  to  four 
times  as  great.  An  abundant  water  supply,  together  with  an  average  tem- 
perature of  over  80°  Fahrenheit,  causes  extremely  rapid  growth.  One  of  the 
bamboo  family,  the  growth  of  which  was  measured  daily,  was  found  to  in- 
crease in  length  on  the  average  nearly  three  inches  in  the  daytime  and  over 
five  inches  during  each  night.  The  moisture  present  in  the  atmosphere 
allows  of  the  growth  of  many  air  plants  (epiphytes),  which  take  the 
moisture  directly  from  the  air  by  means  of  aerial  roots. 


ECOLOGY  149 

The  absence  of  cold  weather  in  tropical  countries  allows  trees  to  mature 
without  a  thick  coating  of  bark  or  corky  material.  The  trees  all  have  a 
green  and  fresh  appearance.  Monocotyledonous  plants  prevail.  Ferns  of 
all  varieties,  especially  the  largest  tree  ferns,  are  abundant. 

Plant  Life  in  the  Temperate  Zones.  —  In  the  state  of  New  York  con- 
ditions are  those  of  a  typical  temperate  flora.  Extremes  of  cold  and  heat  are 
found,  the  temperature  ranging  from  30°  Fahrenheit  below  zero  in  the  win- 
ter to  100°  or  over  in  the  summer.  Conditions  of  moisture  show  an  average 
rainfall  of  from  60  to  130  cm.  Cond'tions  of  moisture  in  the  country  cause 
great  differences  in  the  plant  covering. 

In  the  eastern  part  of  the  United  States  the  rainfall  is  sufficient  to  give 
foothold  to  great  forests,  which  aid  in  keeping  the  water  in  the  soil.  In  the 
middle  West  the  rainfall  is  less,  the  prairies  are  covered  with  grasses  and  other 
plants  which  have  become  adapted  to  withstand  dryness.  In  the  desert 
region  of  the  Southwest  we  find  true  xerophytes,  cacti,  switch  plants, 
yuccas,  and  others,  all  plants  which  are  adapted  to  withstand  almost  total 
absence  of  moisture.  In  the  temperate  zone  the  water  supply  is  the  pri- 
mary factor  which  determines  the  form  of  plant  growth. 

Reference   Books 
for  the  pupil 

Andrews,  Botany  All  the  Year  Round.     American  Book  Company. 
Leavitt,  Outlines  of  Botany.     American  Book  Company. 
Coulter,  Plant  Relations.     D.  Appleton  and  Company. 
Stevens,  Introduction  to  Botany.     D.  C.  Heath  and  Company. 

FOR    the    teacher 

Bailey,  The  Survival  of  the  Unlike.     The  Macmillan  Company. 

Darwin,  Animals  and  Plants  under  Domestication,  Chaps.  IX,  XII.     D.  Appleton 

and  Company. 
Kerner.     Natural  History  of  Plants.     4  Vols.     Henry  Holt  and  Company. 
Schimper,  Plant  Geography.     Clarendon  Press. 
Year  Book,  Department  of  Agriculture,  1894,  1895,  1898,  1900. 


XI.    FLOWERLESS  PLANTS 

Systematic  Botany.  —  The  plant  world  is  divided  into  many  tribes  or 
groups.  Any  one  who  has  visited  a  hothouse  or  a  large  garden  is  likely 
to  notice  this  fact.  And  not  only  are  plants  placed  in  large  groups  which 
have  some  very  conspicuous  characters  in  common,  but  smaller  groupings 
can  be  made  in  which  perhaps  only  a  few  plants  having  common  characters 
may  be  placed.  If  we  plant  a  number  of  peas  so  that  they  will  all  germinate 
under  the  same  conditions  of  soil,  temperature,  and  sunlight,  the  seedlings 
that  develop  will  each  differ  one  from  another  in  a  slight  degree.  But  in  a 
general  way  they  will  have  many  characters  in  common,  as  the  shape  of  the 
leaves,  the  possession  of  tendrils,  form  of  the  flower  and  fruit.  The  smallest 
group  of  plants  or  animals  having  certain  characters  in  common  that  make 
them  different  from  all  other  plants  or  animals  is  called  a  species.  Individuals 
of  such  species  may  differ  slightly;  indeed  no  two  individuals  are  exactly 
alike-  It  is  known  that  in  some  cases  seeds  from  plants  which  have  thus 
varied  to  a  considerable  degree  may  reproduce  these  variations  in  the  young 
plants.  This  fact  is  made  use  of  by  plant  breeders  to  produce  new  kinds 
of  plants. 

Species  are  grouped  together  in  a  larger  group  called  a  genus.  For 
example  many  kinds  of  peas  —  the  everlasting  pea,  the  wild  beach  peas, 
the  sweet  peas,  and  many  others  —  are  all  grouped  in  one  genus  (called 
Lathyrus  or  vetchling)  because  they  have  certain  structural  characteristics 
in  common. 

Nomenclature.  —  When  we  wish  to  identify  a  plant,  we  look  it  up 
by  means  of  its  generic  and  specific  names  in  much  the  same  way  that  we 
look  up  a  name  in  a  city  directory.  As  in  a  directory  the  last  name  of  the 
person  is  placed  first,  as  Jones,  John,  so  we  find  the  Latin  name  Phaseo- 
lus  given  to  the  beans  as  a  genus.  Phaseolus  vulgaris  is  the  name  of  the 
common  bean;  Phaseolus  lunatus,  the  pole  or  lima  bean;  and  Phaseolus 
multiflorus,  the  scarlet  runner. 

System  of  Classification  Artificial.  —  Plant  and  animal  genera  are 
brought  together  in  still  larger  groups,  the  classification  based  on  general  like- 
nesses in  structure.  Such  groups  are  called,  as  they  become  successively 
larger.  Family  or  Tribe,  Order,  and  Class.  Thus  the  whole  plant  and  animal 
kingdom  is  artificially  massed  in  separate  divisions,  the  smallest  of  which  con- 
tains a  few  individuals  very  much  alike ;  and  the  largest  of  which  contains 
very  many  groups  of  individuals,  the  groups  having  some  characters  in 
common.    This  is  called  a  system  of  classification. 

150 


FLOWERLESS  PLANTS  151 

Phanerogams  and  Cryptogams.  —  In  the  widest  sense  the  plant 
world  is  divided  into  two  great  groups,  the  flowering  plants,  or 
Phanerogams,  and  the  flowerless  plants,  or  Cryptogams.  This  is 
an  old  system  of  classification,  but  it  shows  one  very  important 
distinction  in  the  plant  kingdom. 

The  flowerless  plants  are  much  simpler  in  structure  than  the 
flowering  plants.  We  are  apt  to  entirely  overlook  them  in  a 
casual  glance  at  vegetation  in  a  landscape.  Thousands  of  species 
exist  so  small  that  we  cannot  see  them  with  the  unaided  eye. 
Many  kinds  hide  themselves  in  the  water,  while  still  others  may 
lie  flat  on  the  ground  or  cling  to  the  bark  of  trees  and  thus  escape 
observation.  Yet  one  of  the  cryptogams  is  over  a  thousand  feet 
in  length,  one  of  the  longest  plants  in  the  world. 

Classification  of  the  Plant  Kingdom.  —  The  entire  plant  king- 
dom has  been  grouped  as  follows  by  the  later  botanists :  — 

^     ci  ^     7   ^       \  Angiosperrns ,  true  flowering  plants. 

1.  Spermatopm/tes.  ]  ^  ..       .  ,  .i    .      i,. 

(  (jrymno sperms,  the  pmes  and  their  allies. 

2.  Ptendophytes.     The  fern  plants  and  their  allies. 

3.  Bryophytes.     Moss  plants  and  their  allies. 

4.  Thallophyt^s.  Plants  in  which  the  plant  body  is  a  thallus, 
that  is,  the  body  is  not  divided  into  root,  stem,  and  leaves.  A 
seaweed  and  a  mushroom  are  good  examples.  The  Thallophytes 
form  two  groups :  the  Algae  and  the  Fungi. 

The  extent  of  the  plant  kingdom  can  only  be  hinted  at,  because  each  day 
new  species  are  added  to  the  lists.  There  are  about  110,000  species  of  flower- 
ing plants  and  perhaps  half  as  many  flowerless  plants.  The  latter  consist  of 
nearly  3500  species  of  fernlike  plants,  some  16,500  species  of  mosses,  over 
5600  lichens  (plants  consisting  of  a  partnership  between  algse  and  fungi), 
approximately  55,000  species  of  fungi,  and  16,000  species  of  algse. 

Sexual  Reproduction  in  Flowering  Plants.  — Flowering  plants  re- 
produce their  kind  by  the  formation  of  seeds.  As  we  know,  the 
flower  produces  in  the  ovary  structures  which  are  known  as 
ovules.  In  the  interior  of  the  ovule  is  found  a  clear  protoplasmic 
area  which  is  called  the  embryo  sac.  In  this  area  is  a  cell  (the 
egg  cell)  which  is  destined  to  form  the  future  plant.  In  the  pollen 
grain  is  found  another  cell,  the  sperm.     This  cell,  after  the  ger- 


152  BOTANY 

mination  of  the  pollen  grain  on  the  stigmatic  surface  of  the  flower, 
enters  the  ovule  in  the  pollen  tube  and  unites  with  the  egg  cell. 
This  process,  known  as  fertilization,  is  the  most  important  event 
in  the  life  of  the  plant,  for  it  is  only  by  means  of  this  process  that 
the  ovule  is  stimulated  to  become  a  seed.  The  fertilized  egg 
grows  into  the  young  plant  within  the  seed,  known  as  the  embryo 
see  page  34). 

This  method  of  reproduction,  called  sexual  reproduction,  is 
found  in  the  spermatophytes,  that  is,  all  seed-producing  plants. 
In  the  flowerless  plants  a  somewhat  similar  process  takes  place. 
Seeds  are  not  formed,  however,  but  structures  called  spores  repro- 
duce the  plants. 

Sexual  and  Asexual  Spores.  —  A  spore  is  usually  considered  to 

be  a  cell  which  has  become  dormant,  but  which  will  under  favor- 

•   able   conditions   again   germinate   to   form  a  new 

plant.     A  spore,  as  we  shall  see,  may  be  formed  in 

one  of  several  ways.     If  formed  by  the  union  of 

two  cells,  as  is  the  fertilized  egg,  it  is  then  said  to 

mold,  highly     be  a  sexual  spore.     If,  as   is    frequently  the  case, 

magnified.         ^j^^  spore  is  formed  by  the  separation  of  a  bit  of 

protoplasm  from  the  plant  to  form  a  resting  cell,  then  it  is  called 

an  asexual  spore.     In  most  of  the  so-called  "  spore  plants  "  both 

sexual  and   asexual  spores  are  formed  at  different  times  during 

the  life  history  of  the  plant. 

Pteridophytes 

The  Ferns  and  their  Allies.  —  The  fern  plants  include  the  true 
ferns,  the  horsetails  or  scouring  rushes,  and  the  club  mosses.  The 
true  ferns  are  moisture-loving  and  shade -loving  plants;  they  play 
an  important  part  in  the  vegetation  of  the  tropical  forests.  Many 
forms  are  found  in  the  temperate  regions;  we  even  have  some  com- 
mon ferns  that  remain  green  all  winter.  The  ferns  are  among 
the  most  beautiful  of  our  plants,  and  the  study  of  a  common  form 
will  amply  repay  the  time  so  spent. 

The  Polypody   (Polypodium   vidgare)}  —  The  habitat  of  the  polypody 
is  damp  woods  and  rocky  glens.     The  ferns   are  usually  hard  to  get  up 

^  Hunter  and  Valentine's  Manual,  page  93. 


FLOWERLESS   PLANTS 


153 


entire.     The  stem  is  underground.     Large  compound  leaves  (called /ron^/s) 
are  given  off  at  mtervals  along  the  stem.     We  call  the  underground  stem  a 
rootstock.    Try  to  find  a  rea- 
son for  calling  it  a  stem  rather 
than  a  root. 

Note  the  arrangement  of 
the  leaflets,  or  pinnce,  of  the 
fern  frond.  Some  of  the  pinnae 
will  show  a  series  of  little 
brown  dots  on  the  under  sur- 
face. These  structures,  called 
collectively  the  sori  (singular 
sorus),  are  made  up  of  a  num- 
ber of  tiny  spore  cases.  These 
spore  cases,  or  sporangia,  hold 
the  asexual  spores.  Exam- 
ine a  sorus  with  your  hand 
lens  to  make  out  its  position 
on  the  pinna  with  reference 
to  the  veins. 

Mount  a  small  bit  of  the 
fern  leaf  which  contains  a 
sorus  under  a  very  low  power 
of  the  compound  microscope. 
How  are  the  sporangia  ar- 
ranged in  the  sorus  ? 

If  a  single  sporangium  is 
gently  separated  from  the 
mass  and  mounted  carefully 
in  alcohol  and  water  on  a  slide, 
the  following  structures  may 
be  found  :  (a)  the  stalk ;  (5)  a 
thick  wall  row^  of  cells,  yellow 

in  most  specimens,  which  form  the  annulus,  or  ring;    (c)    the  covering  of 

thin-walled  cells  over  the  remainder  of  the 
sporangium.  A  comparison  of  several  spo- 
rangia will  bring  out  the  fact  that  in  an  opened 
sporangium  the  annulus  is  never  broken.  It 
is  always  the  thin-walled  cells  that  are  rup- 
tured. The  dark-colored  spores  may  be  seen 
in  the  opened  sporangia. 


Rock  fern,  polypody.  Notice  the  underground  stem 
giving  off  roots  {R)  from  its  under  surface,  and 
leaves  (C)  from  the  upper  surface.  .The  com- 
pound leaf  or  frond  may  bear  sori  (5)  on  the  under 
side  of  the  leaflets. 


Section  of  sorus;  s,  sporangia; 
i,  indusium,  or  covering;  b, 
blade  of  the  leaf.  —  Wossidlo. 


If  fresh  material  is  obtainable,  it  will  be 
possible  to  see  how  the  spores  get  out  of  the 
sporangium.  A  drop  of  glycerine  run  under  the  cover  slip 
of  a  slide  holding  a  fresh  unopened  sporangium  soon  causes 
the  sporangium  to  snap  open.  If  the  sporangium  is  dry  and 
on  the  under  surface  of  the  fern  leaf,  the  spores  v.ill  be  scattered 
for  a  considerable  distance.  An  explanation  for  this  snapping 
open  of  the  sporangium  is  found  when  we  notice  that  the  outer 
walls  of  the  cells  forming  the  annulus  are  thinner  than  the  inner 
walls.  This  allows  water  to  escape  more  rapidly  on  one  side, 
and  pressure  from  without  causes  the  cells  to  bend  outward        a  sporangium 


154 


BOTANY 


ar_. 


-vh 


Home  Experiment.  —  Plant  some  spores  on  the  surface  of  a  moist  brick 
or  broken  flowerpot.  Cover  them  with  a  piece  of  glass  so  as  to  keep  the 
air  in  which  they  remain  warm  and  moist.  Give  them  moderate  heat 
(about  70°  Fahrenheit) .  After  two  or  three  weeks,  if  the  surface  is  care- 
fully scanned  with  a  hand  lens,  very  tiny  green  threadlike  structures  may 
be  found.     These  structures  grow  rapidly  to  form  flat  heart-shaped  bodies. 

Prothallus.  —  Such  a  structure  is  called  a  prothallus.  The  pro- 
thallus  clings  to  the  surface  of  the  brick  by  means  of  tiny  rootlike 

organs  called  rhizoids.  The 
whole  structure  is  another 
stage  in  the  life  of  the  fern 
plant.  A  careful  examination 
of  the  prothallus  with  a  com- 
pound microscope  reveals  the 
fact  that  scattered  among  the 
rhizoids  are  some  tiny  rounded 
elevations ;  immediately  above 
the  rhizoids  and  between  them 
and  the  little  groove  in  the 
prothallus  are  other  struc- 
tures ;  both  the  above  structures 
are  too  minute  to  find  with 
the  naked  eye. 

Archegonia. — The  last-named  are  called  archegonia;  they  are 
found  to  be  very  tiny  flask-shaped  organs  almost  embedded  in  the 
surface  of  the  prothallus.  Each  archegonium  contains  a  single 
large  cell.     This  we  recognize  as  an  egg  cell. 

Antheridia.  —  The  other  structures  found  among  the  rhizoids  are 
called  antheridia.  Each  antheridium  contains  a  large  number  of 
very  minute  objects  which  are  able  to  move  about  in  water  by 
means  of  lashlike  threads  of  protoplasm.  Each  of  these  motile 
cells  is  called  an  antherozoid;  they  have,  in  fact,  the  same  function 
as  the  sperm  cells  of  the  flowering  plants.  Because  this  part  of 
the  plant  holds  the  egg  cells  and  sperm  cells,  it  is  called  the  sexual 
generation  of  the  fern. 

Fertilization.  —  The  sperm  cells  swim  to  the  egg  cells  in  water 
(rain  or  dew),  being  attracted  to  the  mouth  of  the  flask-shaped 
archegonium  by  an  acid  secretion  which  is  poured  out  by  the  cells 


Prothalium  of  a  common  fern  (Aspidium); 
A,  under  surface,  showing  rhizoids,  rh, 
antheridia.  an,  and  archegonia,  ar;  B,  under 
surface  of  an  older  gametophyte,  showing 
rhizoids,  rh,  and  young  sporophyte,  with 
root,  w,  and  leaf,  h.  (From  Coulter,  Plant 
Structures.) 


FLOWERLESS   PLANTS 


155 


A,  the  archegonium  with  egg  (e)  and  canal  (c); 
B,  antheridium;  C,  antherozoid,  very 
highly  magnified,  —  Strasburger. 


forming  the  neck  of  the  flask.      FertiHzation    is    essentially  the 
same  process  that  has  been  described  for  the  flowering  plants,  the 
sperm    cell    uniting   with   the 
egg  cell  to  form  a  single  cell, 
the  fertilized  egg. 

Sporophyte  and  Gameto- 
phyte.  —  The  direct  result  of 
fertilization  is  the  growth  of 
the  egg  cell  by  repeated  divi- 
sion to  form  a  little  fern  plant. 
Later  the  young  plant  strikes 
root,  the  prothallus  dies  away, 
and  we  have  a  fern  plant  which 
will  later  in  the  season  pro- 
duce asexual  spores.  The 
leafy  fern  plant,  because  it  produces  asexual  spores,  is  called  the 
sporophyte.  The  prothallus,  which  forms  the  eggs  and  sperms, 
both  of  which  are  known  as  gametes,  or  sex  cells,  is  called  the 
gametophyte. 

Alternation  of  Generations.  —  The  fern  plant  during  its  entire 
life  thus  passes  through  two  entirely  different  stages,  or  genera- 
tions. The  spore  germinates  to  form  a  gametophyte,  or  sexual 
generation.  This  sexual  generation  in  turn  produces  an  asexual 
generation,  or  sporophyte.  The  alternation,  in  the  life  history  of  a 
plant  or  animal,  of  a  sexual  stage  with  an  asexual  stage  is  called  an 
alternation  of  generations. 

General  Characters  of  the  Fernlike  Plants.  — These  plants  pass 
through  an  alternation  of  generations ;  they  have  a  distinct  root, 
stem,  and  leaves;  and  the  stem  possesses  conducting  tubes  or  Jibro- 
vascular  bundles;  these  are  the  distinguishing  marks  of  the  ferns 
and  their  allies.  Fern  plants  show  a  great  diversity  in  form 
and  size.  They  vary  from  the  great  tree  ferns  of  the  tropics, 
some  of  which  are  thirty  to  forty  feet  in  height,  to  tiny  forms  of 
almost  microscopic  size.  The  leaves  of  the  ferns  are  among  the 
most  complex  in  form  of  any  that  we  know.  The  position  and 
shape  of  the  spore  cases  differ  greatly  in  different  species  of  ferns; 
,in  some  the  edge  of  the  leaflet  is  modified  to  hold  the  spores,  in 


156 


BOTANY 


others  the  veins  bear  the  spore  cases,  while  in  some  ferns  the 
entire  leaf  is  modified  into  a  spore-bearing  organ. 

The  Horsetails. — This  comprises  a  small  group  of  plants,  recognized  by 
their  erect  habit  of  growth,  the  leaves  coming  out  in  whorls  on  the  stem. 

In  most  forms  the  stem  contains  considerable 
silica.  This  gave  to  the  plant  its  former  use- 
ful place  in  the  household  and  its  name  of 
the  scouring  rush.  If  you  burn  one  of  these 
plants  very  carefully  on  a  tin  plate  over  a 
very  hot  fire,  the  delicate  skeleton  of  silica 
may  be  seen.  The  horsetails,  or  Equisetums, 
were  once  a  very  important  part  of  the  earth's 
vegetation.  Before  the  coal  fields  were  formed 
the  ancestors  of  these  plants  flourished  as 
trees.  A  large  amount  of  the  coal  of  this 
country  is  undoubtedly  formed  from  the 
trunks  of  the  Equisetums  of  the  Carboniferous 
age.  At  present  they  are  represented  by  a 
very  few  species,  none  of  which  are  over  four 
or  five  feet  in  height. 

Club  Mosses. — Another  relative  of  the 
fern  is  the  club  moss  {Lyco'podium) .  It  is 
familiar  to  us  as  a  Christmas  decoration  under 
the  name  of  ground  pine.  It  is  chiefly  of 
interest  now  as  the  representative  of  another 
group  of  plants  that  flourished  during  the 
Carboniferous  age. 

Economic  Value  of  Ferns.  —  It  maybe 
said  that  the  ferns  as  a  group  have  formed  a 
large  part  of  the  enormous  deposits  of  almost 
pure  carbon  that  we  call  coal,  from  which  we 
now  derive  the  energy  to  run  our  many  en- 
gines. 

Bryophytes 


An  eqmsetum,  about  one  half 
natural  size. 


Mosses,  like  ferns,  are  shade-loving 
and  moisture-loving  plants.  They  form 
velvety  carpets  in  many  of  our  forests, 
but  they  often  show  their  preference  for  moist  localities  by  cover- 
ing the  wooded  shores  of  lakes  and  swamps. 

Pigeon-wheat  Moss.  —  One  of  the  mosses  frequently  seen  and 
easily  recognized  is  the  so-called  pigeon-wheat  moss  {Polytrichum 


FLOWERLESS   PLANTS 


157 


«\Tn  1 

'  f 

kl 

Ql^ 

A  group  of  moss  plants,  showing  the  stalk  (»S.)  and 
capsule  (C.)  of  the  spore-forming  generation. 


commune)}  Unlike  some  mosses,  it  often  inhabits  dry  localities. 
It  may  be  found  on  some  dry  hillock  close  to  the  edge  of  the  woods 
where  it  forms  a  reddish  brown  carpet.  This  red  color  is  due 
largely  to  the  presence  of  a  great  number  of  little  upright  stalks, 
bearing  at  the  summit 
tiny  capsules,  which 
seem  to  grow  up  from 
the  leafy  moss  plant. 
The  resemblance  of  a 
large  number  of  these 
stalks  and  capsules  to 
a  mimic  field  of  grain 
has  given  the  name 
pigeon-wheat  moss  to 
this  form.  Take  home 
some  of  the  moss  plants 
for  study  in  the  labora- 
tory. Take  care  to 
find  not  only  the  plants  bearing  stalk  and  capsule,  but  also  certain 
plants  which  terminate  in  a  tiny  rosette  of  leaves,  this  inclosing 
what  seems  to  be  a  very  small  flower. 

Leafy  Moss  Plant.  —  An  examination  of  a  leafy  moss  plant  will  show 
that  it  has  rhizoids  or  hairlike  roots,  an  upright  stem,  and  green  leaves. 
Make  a  drawing  to  show  all  the  parts. 

Notice  the  stalk  and  capsule  closely.  The  stalk  grows  directly  from  the 
end  of  the  leafy  plant.  This  capsule  is  provided  with  an  outer  cap.  The 
cap,  or  calyptra,  as  it  is  called,  seems  to  have  somewhat  the  structure  of  a 
thatched  roof.  Under  the  cap  is  found  a  lid,  or  cover,  to  the  capsule.  Re- 
move the  cover  very  carefully;  notice  whether  it  is  attached  to  the 
capsule.  NoAv,  turning  the  capsule  upside  down,  tap  it  gently  against  the 
surface  of  your  drawing  paper.  The  dust  that  escapes  is  made  up  of  a 
great  number  of  spores. 

Sporophyte. — The  capsule  is  the  sporangium  of  the  moss  plant.  The 
stalk  and  capsule  together  form  the  sporophyte  of  the  moss. 

If  we  were  to  plant  the  spores  of  the  moss  in  damp  sand,  taking  care  to 
keep  the  sand  moist  and  warm,  we  might  obtain  germinating  spores.  The 
spore  germinates  into  a  threadlike  structure,  very  tiny,  and  not  at  all  like 
the  adult  moss  plant.     This  thread  is  called  a  protonema. 

*  See  Hunter  and  Valentine,  Manual,  page  90. 


158 


BOTANY 


Adult  Moss  Plants.  —  It  soon  develops  rhizoids;  tiny  buds  appear  that 
in  time  form  the  adult  moss  plant.  These  adult  plants  may  grow  only 
leaves,  and  become  what  are  known  as  sterile  plants;  or  they  may  develop 
into  a  plant  that  bears  at  the  summit  the  little  rosette  of  leaves  previously 
referred  to.  Within  the  rosette  lie  a  number  of  tiny  organs  which  resemble 
the  antheridia  of  the  ferns  in  structure.  They  are  in  fact  antheridia  and 
hold  large  numbers  of  sperm  cells.  Other  moss  plants  bear  at  the  summit 
of  the  stem  a  tuft  of  leaves  which  hide  a  number  of  small  flask-shaped 
archegonia.    The  archegonia  contain  each  a  single  egg  cell.     These  plants 

form  the  sexual  generation  of  the  moss.  After 
a  sperm  cell  has  been  transferred  to  the  egg 
cell  a  fusion  of  the  two  cells  takes  place. 
This,  we  remember,  is  the  process  of  fertili- 
zation. In  the  mosses  as  well  as  the  ferns 
the  fertilization  of  the  egg  cell  results  in  the 
growth  of  that  part  of  the  plant  which  forms 
and  bears  the  asexual  spores. 

Alternation  of  Generations.  —  In  the 

mosses  also  we  have  an  alternation 
of  generations.  The  leafy  moss,  bear- 
ing among  its  leaves  the  sex  organs, 
antheridia  and  archegonia,  gives  place 
to  a  stalk  and  capsule  bearing  the 
asexual  spores.  This  spore-bearing 
portion  of  the  plant  does  not  appear 
until  after  fertilization;  then  it  grows 
directly  out  of  that  part  of  the  plant 
that  produces  the  egg  cell.  In  fact, 
if  we  make  a  microscopic  examination 
of  this  archegonium  directly  after  fer- 
tilization, we  find  that  the  sporo- 
phyte  is  a  direct  outgrowth  from  the 
fertilized  egg  cell. 

Sporophyte  a  Parasite.  —  One  interest- 
ing fact  comes  out  in  connection  with 
this  growth  of  the  sporophyte.  It  has 
no  green  leaves  and  must  therefore  obtain  all  its  nourishment  from 
the  leafy  moss  plant,  or  gametophyte.  The  spore-bearing  part  of 
the  plant  is  thus  actually  a  parasite  upon  the  gametophyte. 


Pigeon  wheat.  A  moss  showing 
egg-bearing  gametophyte  and 
sporophyte  (stalk  and  capsule), 
the  latter  entirely  dependent 
upon  the  former. 


FLOWERLESS   PLANTS  159 

The  Liverworts.  —  Liverworts  are  mosslike  plants  which  inhabit  moist 
localities,  some  living  in  or  on  the  surface  of  water,  others  on  rocks  or 
damp  soil,  and  some  even  growing  on  the  bark  of  trees.  The  liverworts 
have  an  irregular  thallus-shaped  or  platelike  body.  Rhizoids  are  developed 
from  the  lower  surface  of  the  body.  From  the  plant  body  arise  upright 
structures  which  bear  the  antheridia  and  archegonia. 

Their  life  history  is  nearly  that  of  a  moss.  These  plants  may  also  re- 
produce themselves  asexually  by  means  of  budlike  structures  called  gemmce, 
The  gemmae,  which  are  formed  in  cup-shaped  organs  on  the  upper  suiface 
of  the  plant,  break  off  and  under  favorable  conditions  may  form  a  new- 
plant. 

Economic  Value  of  Mosses. — The  mosses  and  their  allies  have  little 
direct  economic  value.  Indirectly  they  are  of  much  benefit  to  mankind.  In 
many  localities  they  form  a  soft  carpet,  which  is  of  great  importance  in 
holding  water  in  the  soil;  thus  they  prevent  erosion.  They  give  off  not  a 
little  oxygen  to  the  atmosphere  and  must  use  considerable  carbon  dioxide 
in  their  manufacture  of  starch, 

Thallophytes 

We  have  already  defined  a  thallus  as  a  plant  body  which  has 
no  definite  root,  stem,  or  leaf.  It  may  be  platelike,  ribbon- 
shaped,  threadlike,  globular,  or  even  irregular  in  form. 

The  thallus  plants  may  be  grouped  in  two  great  divisions: 
the  Algce,  water-loving  thallophytes  containing  chlorophyll,  and  the 
Fungi,  thallus  plants  which  do  not  contain  chlorophyll. 

Fungi,  Parasites,  and  Saprophytes.  —  As  a  direct  result  of  the 
lack  of  chlorophyll  in  the  cells,  the  fungi  are  unable  to  make  their 
own  food.  They  must  obtain  food  from  other  plants  or  animals. 
Some  take  up  their  abode  upon  living  plants  or  animals  (in  which 
case  they  are  called  parasites) ;  others  obtain  their  food  from  some 
dead  organic  matter.  The  latter  are  called  saprophytes.  The  above 
facts  make  the  group  of  the  fungi  of  immense  economic  impor- 
tance to  man.  Much  of  the  space  devoted  to  the  fungi  will  be 
given  up  to  a  consideration  of  the  relation  of  parasitic  and  sap- 
rophytic plants  to  their  hosts,  the  living  or  dead  organisms  from 
which  they  obtain  their  food. 

Mold.  —  One  of  the  most  common  of  all  our  fungi  is  the  black  mold 
(Rhizopus  nigricans) . 

Experiments  to  determine  the  Growth  of  Mold.  —  Place  a  piece  of  bread 
in  each  of  two  wide-mouthed  bottles  or  jars,  add  a  little  water,  and  ex- 


160 


BOTANY 


Experiment  with  mold  on  bread;  ^,  in  a  living 
room;  B,  in  an  ice-box;  C,  above  the  stove  in  a 
kitchen. 


pose  both  jars  to  the  air  of  the  living  room  or  kitchen  for  five  minutes. 
Then  cover  both  jars  and  plunge  one  into  boiling  water  for  a  few  minutes. 
Now  place  the  jars  side  by  side  in  a  moderately  warm  room  for  two  or  three 
days.     In  which  jar  does  growth  appear  first?     Do  both  jars  have  like 

growth  of  mold  in  the  given 
period  of  time  ? 

Other  experiments  may  be 
performed  to  show  the  rela- 
tion of  the  growth  of  mold  to 
light,  to  different  degrees  of 
moisture  and  to  different  tem- 
peratures. Why  do  things 
get  moldy  in  a  damp  locality 
quicker  than  in  a  dry  one  ? 
How  Avould  you  account  for 
the  growth  of  mold  inside  of 
a  jar  of  preserves  or  jelly? 
Can  you  determine  by  experi- 
ment whether  black  mold  uses 
oxygen  in  its  growth? 

Directions  for  Growth  of 
Mold.  —  Bread  mold  may  be 
conveniently  grown  for  laboratory  use  in  small  shallow  dishes  (Syracuse  watch 
glasses,  Petri  dishes,  or  butter  chips) .  If  bread  is  exposed  to  the  air  for  a  few 
minutes  and  then  left  in  the  covered  dishes  for  a  day  or  two,  with  a  bit  of  wet 
sponge  or  blotting  paper  in  the  dish  to  keep  the  air  moist,  a  good  supply 
of  mold  may  be  obtained  in  a  convenient  dish  for  observational  purposes.^ 

Observations  on  Mold.  —  Examine  the  tangled  mass  of  threads  which 
cover  the  bread.  This  is  called  the  mycelium,  each  thread  being  called  a 
hypha.  How  do  the  hyphae  appear  to  be  attached  to  the  bread?  Many  of 
the  hyphse  are  prolonged  into  tiny  upright  threads,  bearing  at  the  top  a  little 
ball.  With  the  low  power  of  the  microscope  the  structure  of  a  sporangium 
may  be  made  out.  The  dark-colored 
ones  are  full  of  ripe  spores,  which 
may  be  seen  by  lightly  tapping  the 
cover  slip  over  the  slide.  How  do 
the  spores  normally  get  out  of  the 
sporangium?  Try  to  find  some 
young  sporangia  and  note  the  differ- 
ences in  size  and  color  between  them 
and  the  older  ones.  Draw  a  series 
of  sporangia  as  seen  under  the  low 
power. 

This  method  of  the  produc- 
tion of  spores  is  evidently  asex- 
ual. These  spores,  if  grown 
under  favorable  conditions,  will 


■--'••lyilllVi'nii"' 


Bread  mold;  r,  rhizoids;  s,  sporangium. 


produce  more  mycelia,  which  in  turn  bear  sporangia.  It  has  been 
found,  however,  that  at  some  time  during  the  life  of  the  mold 
another  method  of  reproduction  is  likely  to  occur. 

'  See  Hunter  and  Valentine,  Manual,  page  83. 


FLOWERLESS   PLANTS 


161 


Formation  of  Zygospores.  — Two  hyphae  which  are  close-lying  put 
out  threads  which  communicate.  The  end  of  each  of  the  threads 
cuts  off  a  cell,  and  the  two  cells,  each  from  a  different  hypha, 
flow  together  and  mingle.  In  this  condition  they  remain  as  a  single 
resting  cell.  This  cell,  which  puts  a  heavy  wall  around  itself,  is 
called  a  zygospore.  In  the  process  we  called  fertilization,  we  found 
that  the  two  cells  which  united  to  form  one  cell  were  of  dif- 
ferent sizes.  Here  the  cells  are  of  the  same  size.  When  two  cells 
of  the  same  size  unite  to  form  a  single  cell,  we  call  the  process  conjuga- 
tion. The  ultimate  result  of  the  conjugation  of  the  two  cells  is 
that  a  new  plant  grows  from  the  zygospore  after  a  period  of  rest. 
During  the  resting  stage  a  b 

the  spore  may  undergo 
veiy  unfavorable  condi- 
tions, even  to  extreme 
dryness,  heat,  or  cold. 
The  use  of  the  zygospore 
to  the  plant  is  evidently 
to  continue  the  species 
during  an  unfavorable 
time  in  the  life  history 
of  the  plant.  The  pro- 
cess of  conjugation  is 
probably  a  sexual  process.  Its  significance  is  not  well  under- 
stood.^    Is  there  then  an  alternation  of  generations  in  the  mold  ? 

Physiology  of  the  Growth  of  Mold.  —  Mold,  in  order  to  grow 
rapidly,  evidently  needs  considerable  moisture  and  heat.  It  ob- 
tains its  food  from  the  material  on  which  it  lives.  This  it  is  able 
to  do  by  means  of  digestive  ferments,  which  are  given  out  by 
the  rhizoids  or  rootlike  parts  of  the  hyphae,  by  means  of  which  the 
mold  clings  to  the  bread.  These  digestive  ferments  change  the 
starch  of  the  bread  to  sugar,  and  change  the  proteids  into  a  form 
that  can  be  osmosed  into  the  hyphae.  Thus  the  plant  is  enabled 
to   absorb   the    material.      The    foods    are    then    changed    into 


Conjugation  of  black  mold;  A,  B.  (',  D.  successive 
stages  in  the  formation  of  the  zygospore. 


*  It  seems  to  have  been  proved  recently  that  zygospores  are  formed  by  the 
union  of  two  cells,  from  different  filaments,  one  of  which  has  male,  the  other  female 
characters. 


HUNTER  S   BIOL. 


11 


IG2 


BOTANY 


Spore  print. 

of  the  cap.  These  are  the  gills, 
gills  downward  on  the  surface  of 
disturb  for  at  least  twelve  hours, 
it  will  be  found  that  when  the  cap 
is  removed  a  print  of  the  shape 
and  size  of  the  gills  remains  on 
the  paper.  This  is  a  spore  print. 
It  has  been  caused  by  the  spores 
of  the  plant,  which  have  fallen 
from  the  place  where  they  were 
formed  between  the  gills  to  the 
surface  of  the  paper. 

Mycelium.  —  The  mushroom 
is,  then,  the  spore-bearing  part 
of  the  plant.  Where  is  the  plant 
body?  This  question  is  an- 
swered if  we  dig  up  a  little  of 
the  earth  surrounding  a  mush- 
room. In  the  rich  black  soil  is 
seen  a  mass  of  little  whitish 
threads.  These  threads  form  the 
mycelium  of  the  fungus.  The 
hyphae  of  this  part  of  the  plant 
body  take  food  from  the  organic 
matter  in   the   soil    and    digest 


protoplasm  or  used  to 
produce  energy.  This 
seems  to  be  the  usual 
method  by  which  sapro- 
phytes assimilate  the 
materials  on  which  they 
live. 

Other  Saprophytic 
Fungi. — The  mushroom  re- 
sembles a  tiny  umbrella.  The 
upper  part  is  known  to  bot- 
anists as  the  cap;  the  cap  is 
held  up  by  a  stalk  or  stipe. 
The  under  surface  of  the  cap 
discloses  a  number  of  struc- 
tures which  radiate  out  from 
the  central  stipe  to  the  edge 
If  you  place  the  cap  of  a  mushroom 
a  piece  of  white  paper,  being  careful  not  to 


Mushrooms:  the  younger  specimen,  at  the  right, 
shows  the  mycehum.    Photographed  by  Overton 


FLOWERLESS   PLANTS 


163 


it  in  the  same  manner  as  did  the  hyphse  of  black  mold.     The  mushroom  is 
a  saprophyte.     No  sexual  stage  has  yet  been  discovered. 

Poisonous  Mushrooms.  —  Fungi  of  the  mushroom  species  are  classed  by 
botanists  as  edible  and  inedible.  The  latter  are  popularly  known  as  toad- 
stools. It  is  difficult  to  give  the  beginner  any  stated  rules  by  which  to 
distinguish  the  inedible  from  the  edible  species.  A  few  general  rules  may 
be  given,  however,  to  the  collector:  — 

Do  not  use  mushrooms  that  are  old  or  black. 

Never  collect  those  with  swollen  bases  surrounded  with  saclike  or  scaly 
envelopes.  (Such  a  structure  forms  the  so-called  death  cup  of  the  deadly 
Amanita.) 

Do  not  collect  mushrooms  in  the  early  stage  known  as  buttons. 

Do  not  use  mushrooms  with  a  milky  juice. 

Avoid  fungi  with  a  weblike  ring  around  the  upper  part  of  the  stipe. 
Be  very  cautious  about  trying  new  varieties.  Better  learn  one  or  two 
edible  species  and  stick  to  them.  Beginners  may  safely  eat  any  of  the 
club  or  coral  fungi  found  growing  on  dead  trees  in  damp  woods ;  also  young 
puffballs  and  the  morels,  with 
their  characteristically  ridged  sur- 
face. 

Food  Value  of  Mushrooms. — 
The  food  value  of  the  edible 
mushroom  has  been  much  over- 
estimated. Recent  experiments 
seem  to  show  that,  although  they 
have  a  slight  food  value,  they  are 
far  from  taking  the  place  of  ni- 
trogenous foods,  as  was  formerly 
believed  by  scientists. 

Shelf  Fungus.  —  A  near  rela- 
tion to  the  mushroom  is  the 
bracket  or  tree  fungus.  This  fun- 
gus is  familiar  to  any  one  who  has 
been  in  a  forest  in  this  part  of  the 
country. 

An  examination  of  specimens 
shows  that  the  shelf  or  bracket  is 
in  reality  a  spore  case,  which  is 
usually  provided  with  a  very  con- 
siderable number  of  holes,  slits,  or 
pores  in  which  the  spores  are 
fonned.     The  spores,  when  ripe, 


Shelf  or  bracket  fungi  on  dead  tree  trunk. 
Photographed  by  Overton. 


escape  from  the  under  surface  of  the  spore-bearing  body  through   the 
minute  pores.     The  mycelium  is  within  the  tissue  of  the  tree.     Remove 


164  BOTANY 

the  bark  from  any  tree  infected  with  bracket  fungus,  and  you  will  find  the 
silvery  threads  of  the  mycelium  sending  their  greedy  hyphae  to  all  parts  of 
the  wood  adjacent  to  the  spot  first  attacked  by  the  fungus.  This  fungus 
begins  its  life  by  the  lodgment  of  a  spore  in  some  part  of  the  tree  which  has 
become  diseased  or  broken.  Once  established  on  its  host,  it  spreads  rapidly. 
There  is  no  remedy  except  to  kill  the  tree  and  burn  it,  so  as  to  burn  up  the 
spores.  Many  fine  trees,  sound  except  for  a  slight  bruise  or  other  injury, 
are  annuallj'"  infected  and  eventually  killed.  In  cities  thousands  of  trees 
become  infected  through  careless  hitching  of  horses  so  that  the  horse  may 
gnaw  or  crib  on  the  tree,  thus  exposing  a  fresh  surface  for  the  growth  of 
spores. 

Field  Work.  —  A  field  trip  to  a  park  or  grove  near  home  will  show  the 
great  destruction  of  timber  by  this  means.  Count  the  number  of  perfect 
trees  in  a  given  area.  Compare  with  the  number  of  trees  attacked  by  the 
fungus.  Does  the  fungus  appear  to  be  transmit; ted  from  one  tree  to  a  tree 
near  at  hand  ?  In  how  many  instances  can  you  discover  the  point  where 
the  fungus  first  attacked  the  tree  ? 

Parasitic  Fungi.  —  Of  even  more  importance  are  the  fungi  that 
attack  a  living  host.  The  most  important  of  such  plants  from 
an  economic  standpoint  are  the  rusts,  smuts,  and  mildews  which 

prey  upon  grain,  corn,  and 
other  cultivated  plants. 
Some  of  these  are  also 
parasitic  upon  fruit  and 
shade  trees.  Damage  ex- 
tending to  hundreds  of 
millions  of  dollars  is  annu- 

Corn  smut,  a  fungus  parasitic  on  corn;  the  black  „ii„  Afxnc^  hir  f  Itaqa  -nlanf « 

mass  consists  almost  entirely  of  ripe  spores.  ^^V    ^^'^^  ^y  Lnese  pidms. 

Wheat  Rust. — Wheat  rust  is  probably  the  most  destructive  parasite  in 
the  world.  For  hundreds  of  years  wheat  rust  has  been  one  of  the  most 
dreaded  of  plant  diseases,  because  it  destroys  the  one  harvest  upon  which 
the  civilized  world  is  most  dependent.  For  a  long  time  past  the  ap- 
pearance of  rust  has  been  associated  with  the  presence  of  barberry  bushes 
in  the  neighborhood  of  the  wheat  fields.  Although  laws  were  enacted  nearly 
two  hundred  years  ago  in  New  England  to  provide  for  the  destruction  of  bar- 
berry bushes  near  infected  wheat  fields,  nothing  was  actually  known  of  the 
relation  existing  between  the  rust  and  the  barberry  until  recently.  It  was 
then  proved  beyond  doubt  that  the  wheat  rust  passed  part  of  its  life  as  a 
parasite  on  the  barberry  and  from  it  passed  to  the  wheat  plant.  If  a  blade 
of  wheat  infected  with  rust  is  examined  early  in  the  summer,  the  leaf 
blade  will  show  a  collection  of  reddish  brown  spots  or  streaks.     These 


FLOWERLESS   PLANTS 


165 


Uredospores  and  a  teleuto- 
spore  (/)  of  wheat  rust. — 
De  Bary, 


spots  are  caused  by  collections  of  spores  of  the  rust.  The  mycelium  of  the 
plant  is  within  the  blade  of  the  leaf,  where  it  takes  its  food  supply  from  the 
living  cells  of  the  green  leaf.  The  mycelium 
sends  up  stalks  through  the  stomata  of  the  leaf  ; 
it  is  these  that  hold  the  sporangia,  filled  with 
myriads  of  yellow-brown  spores.  The  spores 
produced  in  the  summer  time  are  thin-walled 
and  easily  blown  by  the  wind;  wherever  they 
alight  on  a  wheat  plant,  there  they  germinate  to 
form  another  mass  of  hyphse  within  the  leaf. 
These  parasites  again  produce  more  of  the  uredo- 
spores, as  the  summer  spores 

are  called.    In  the  early  fall 

the  rust,  instead  of  forming 

thin-walled  spores,  produces 

a    curious,    double,     thick- 
walled   spore    in    its    place. 

This  spore,  known  as  a  te- 

leutospore,  remains  dormant 

during  the  winter.     In  the 

early   spring    it   germinates 

wherever  it  happens  to  have 

fallen,  as  it  is  not  at  this  stage  a  true  parasite.     Upon 

germination  it  forms  a  threadlike  body.     On  this  body 

are   formed  tiny  sporelike 

structures  which  have  been 

named  sporidia.     The  spo- 

ridia  germinate  only  upon 

the   barberry,   where   they 

form  a  mycelium  within  the 

leaf. 

This      mycelium      soon 

forms  little  masses  of  spore 

cases  which,  because  of 
their  appearance,  are  called  cluster  cups.  The 
cluster  cups  may  easily  be  seen  with  the  naked 
eye  on  the  surface  of  the  infected  barberry  leaf. 
Spores  from  the  cluster  cups  are  carried  by  the 
wind  to  a  neighboring  wheat  field,  and  there 
germinate  upon  the  blade  of  wheat,  to  form  the 
parasite  we  have  already  called  wheat  rust. 
In  some  cases  the  cluster-cup  stage  appears  to 
be  left  out  of  the  life  cycle,  the  sporidia  germinating  directly  upon  the 
wheat  plants. 


Teleutospore  germi- 
nating and  form- 
ing sporidia,  s,  s. 
(From  Coulter, 
Plant  Structures.) 


Section  through  a  cluster  cup 
of  wheat  rust  in  the  leaf  of 
barberry. 


166 


BOTANY 


A   perithecium  broken 
open  to  show  the  asci. 


Mildews.  —  Another  group  of  fungi  that  are  of  considerable  economic 
importance  is  made  up  of  the  sac  fungi.  Such  fungi  are  commonly  called 
mildews.  Some  of  the  most  easily  obtained  specimens  come  from  the  lilac, 
rose,  or  willow.     These  fungi  do  not  penetrate  the  host  plant  to  any  depth, 

but  cover  the  leaves  of  the  host  with  the  whitish 
threads  of  the  mycelium.  Hence  they  may  be  killed 
by  means  of  applications  of  some  fungus-killing  fluid, 
as  Bordeaux  mixture.^  They  obtain  their  food  from 
the  outer  layer  of  cells  in  the  leaf  of  the  host. 
These  mildews  produce  a  spore-bearing  portion 
known  as  a  'perithecium.  When  the  perithecium 
becomes  broken,  a  number  of  little  sacs  containing 
the  spores  are  released.  Each  sac  is  called  an 
ascus,  and  the  spores  contained  within  are  ascospores. 
Each  ascospore  may  germinate  to  form  a  new  plant. 
Among  other  useful  plants  preyed  upon  by  this  group 
of  fungi  are  the  plum,  cherry,  and  peach  trees.  (The  diseases  known  as 
black  knot  and  peach  curl  are  thus  caused.)  Other  sac  fungi  are  the  morels 
and  truffles,  the  downy  mildews,  blue  and  green  molds,  and  many  other 
forms.  One  important  member  of  this  group  is  the  tiny  parasite  found 
on  rye  and  other  grains,  which  gives  us  the  drug  ergot. 

Yeast. — Although  as  a  group  the  fungi  are  harmful  to  man  in  the 
economic  sense,  nevertheless  there  are  some  fungi  that  stand  in  a  decidedly 
helpful  relationship  to  the  human  race.  Chief  of  these  are  the  yeast  plants. 
Yeasts  are  found  to  exist  in  a  wild  state  in  very  many  parts  of  the  world. 
They  are  found  on  the  skins  of  fruits,  in  the  soil  of 
vineyards  and  orchards,  in  cider,  beer,  and  other 
fluids,  while  they  may  exist  in  a  dr.y  state  almost 
any^vhere  in  the  air  around  us.  In  a  cultivated 
state  w^e  find  them  doing  our  work  as  the  agents 
which  cause  the  rising  of  bread,  and  the  fermenta- 
tion in  beer  and  other  alcoholic  fluids. 

Size  and  Shape,  Manner  or  Growth,  etc.  — 
The  common  compressed  yeast  cake  contains  mil- 
lions of  these  tiny  plants,  easily  the  smallest  we  have 
yet  studied.  In  its  simplest  form  a  yeast  plant  is 
a  single  cell.  If  you  shake  up  a  bit  of  a  compressed 
yeast  cake  in  a  mixture  of  sugar  and  water  and 
then  examine  a  drop  of  the  milky  fluid  after  twenty- 
four  hours  have  elapsed,  it  will  be  found  to  contain 
vast  numbers  of  yeast  plants.  The  shape  of  such  a  plant  is  ovoid.  Notice 
the  granular  appearance  of  the  protoplasm  of  which  it  is  formed.     Look 


A,  yeast  plant  bud  just 
forming;  B,  bud  al- 
most ready  to  leave 
parent  cell.  Note  the 
nucleus  (A'')  dividmg 
into  two  parts.  After 
Sedgwick  and  Wilson. 


^  See  Goff  and  Mayne,  First  Principles  of  Agriculture,  page  59,  for  formiila  of 
Bordeaux  mixture. 


FLOWERLESS   PLANTS  167 

for  tiny  clear  areas  in  the  cells;  these  are  vacuoles,  or  spaces  filled  with 
fluid.  The  nucleus  is  hard  to  find  in  an  unstained  yeast  cell;  it  can,  how- 
ever, be  found  in  specimens  which  have  been  prepared  by  staining  the  .pre- 
viously killed  cells  with  iron-haematoxylin.  (See  Lee,  Vade  Mecum  or 
Sedgwick  and  Wilson,  General  Biology.)  Yeast  cells  grow  rapidly  and  re- 
produce by  a  process  of  budding.  Look  for  cells  with  smaller  cells  attached. 
Is  there  ever  more  than  one  cell  budded  off  from  a  parent  ? 

Draw  several  cells,  showing  buds  as  they  appear  to  you  under  the  high 
power  of  the  compound  microscope. 

Spore  Formation.  —  Most  yeast  plants  seem  to  produce  spores  at  some 
time  during  their  existence.  The  spores  are  formed  within  a  yeast  cell, 
as  many  as  four  being  produced  within  a  single  cell.  These  spores,  under 
proper  conditions,  will  germinate  and  form  new  plants.  The  yeast  forms 
ascospores. 

Conditions  Favorable  to  Growth  of  Yeast. —  Under  certain  conditions 
yeast,  when  added  to  dough,  will  cause  it  to  rise.  We  also  know  that  yeast 
has  something  to  do  with  the  process  we  call  fermentation.  The  following 
experiments  will  throw  some  light  on  these  points:  — 

Label  three  pint  fruit  jars  A,  B,  and  C.  Add  one  fourth  of  a  compressed 
yeast  cake  to  two  cups  of  water  containing  two  tablespoonfuls  of  molasses 
or  sugar.  Stir  well  and  divide  into  three  equal  parts.  Place  one  portion 
in  each  jar.  Put  one  jar  in  the  ice  box  on  the  ice,  and  one  over  the 
kitchen  stove  or  near  a  radiator;  boil  the  third  jar  by  immersing  it  in  a 
dish  of  boiling  water,  and  place  it  next  to  B.  Lay  the  covers  on  the 
jars.  After  twenty-four  hours,  look  to  see  if  any  bubbles  have  made  their 
appearance  in  any  of  the  jars.  Notice  the  color,  taste,  and  odor  of  each  jar. 
Lower  a  lighted  match  in  a  jar  in  which  bubbles  are  rising.  What  gas  is 
formed  by  the  growth  of  yeast  ? 

This  experiment  shows  that  yeast  plants,  like  most  other  forms  of  plant 
life,  will  not  grow  in  a  cold  atmosphere,  and  that  they  may  be  killed  by 
too  much  heat.  They  grow  freely  in  solutions  containing  sugar.  Experi- 
ments may  be  performed  to  test  whether  they  will  grow  in  distilled  water 
(which  contains  no  organic  matter),  and  as  to  their  growth  in  pond  water. 
They  thrive  in  a  solution  containing  compounds  of  nitrogen,  named  after  its 
discoverer,  Pasteur's  solution.^  Yeasts  are  saprophytes.  In  order  to  grow, 
they  must  be  supplied  with  food  materials  that  will  build  up  protoplasm 
as  M^ell  as  release  energy. 

Fermentation  A  Chemical  Process. — In  this  process  of  growth  the  sugar 
of  the  solution  in  which  they  live  is  broken  up  by  a  digestive  ferment  or 

^  The  formula  is  :  — 

838  c.c.  distilled  water. 

10  c.c.  .......  ammonium  tartrate. 

150  c.c.  saturated  solution  of  grape  sugar. 

2  grams magnesium  sulphate. 

2  grams calcium  phosphate. 

2  grams potassium  phosphate. 


168  BOTANY 

enzyme  into  carbon  dioxide  and  alcohol.  This  may  be  expressed  by  the 
following  chemical  formula:  C6H12O6  =2  (C2H60)  +  2  (CO2).  This  means 
that  the  sugar  forms  alcohol  and  carbon  dioxide.  This  process,  which  we 
call  fermentation,  is  of  the  greatest  importance  in  the  brewing  industry. 

Beer  Making.  —  Brewers'  yeasts  are  cultivated  with  the  greatest  care; 
for  the  different  flavors  of  beer  seem  to  depend  largely  upon  the  condition 
of  the  yeast  plants.  Beer  is  made  in  the  following  manner:  Sprouted 
barley,  called  malt,  in  which  the  starch  of  the  grain  has  been  changed  to 
grape  sugar  by  a  process  of  digestion,  is  killed  by  drying  in  a  hot  kiln. 
Then  hops  are  added  to  give  the  mixture  a  bitter  taste.  Now  comes  the 
addition  of  the  yeast  plants,  which  multiply  rapidly  under  the  favorable 
conditions  of  food  and  heat.  Fermentation  results  on  a  large  scale  from 
the  breaking  down  of  the  grape  sugar,  the  alcohol  remaining  in  the  fluid, 
the  carbon  dioxide  passing  off  into  the  air.  The  process  is  stopped  at  the 
right  instant,  and  the  beer  is  stored  either  in  bottles  or  casks. 

In  bread  making  the  rapid  growth  of  the  yeast  plants  is  facilitated  by 
placing  the  pan  containing  the  mixture  in  a  warm  place  over  night.  Fer- 
mentation results  from  the  rapid  growth  of  the  yeast  in  the  dough;  the 
carbon  dioxide  remains  as  the  bubbles  so  familiar  to  the  bread  maker, 
making  the  bread  light  and  more  digestible;  the  alcohol  produced  is  evapo- 
rated during  the  process  of  baking. 

Bacteria.  —  The  bacteria  are  found  in  the  earth,  the  water, 
and  the  air.  ''  Anywhere  but  not  everywhere,"  as  one  writer 
has  put  it.  They  swarm  in  stale  milk,  in  impure  water,  and  in 
any  decaying  material. 

These  tin}^  plants,  "  man's  invisible  friends  and  foes,"  are  of 
such  importance  to  mankind  that  thousands  of  scientists  devote 
their  whole  lives  to  their  study,  and  a  science  called  bacteriology 
has  been  named  after  them. 

Size  and  Form.  —  In  size,  bacteria  are  the  most  minute  plants 
known.  A  bacterium  of  average  size  is  about  -^-^0  of  an  inch  in 
length,  and  perhaps  ysiro  o"  ^^  ^^  ^^^^  i^  diameter.  Some  species 
are  much  larger,  others  smaller.  A  common  spherical  form  is 
.^oVo  ^^  ^n  ii^ch  in  diameter.  It  will  mean  more  to  us,  perhaps, 
if  we  remember  that  several  millions  of  bacteria  of  average  size 
may  be  placed  within  the  area  formed  in  this  letter  0.  Three 
well-defined  forms  of  bacteria  are  recognized:  a  spherical  form 
called  a  coccus,  a  rod-shaped  bacterium,  the  bacillus,  and  a  spiral 
form,  the   spirillum.      Most  bacteria  are   capable  of   movement 


FLOWERLESS   PLANTS 


169 


when  living  in  a  fluid.  Such  movement,  seems  to  be  caused 
by  tiny  lashlike  threads  of  protoplasm  called  cilia.  The  cilia 
project  from  the  body,  and  by  a  rapid  movement  cause  locomotion 
to  take  place.  Bacteria  reproduce  with  almost  incredible  rapidity. 
It  is  estimated  that  a  single  bacterium,  by 
a  process  of  division  called  fission,  will  give 
rise  to  over  16,700,000  others  in  twenty- 
four  hours.  Dr.  Prudden  has  estimated  that 
such  a  bacterium,  if  allowed  to  develop  un- 
checked for  five  days,  would  fill  all  the 
oceans  of  this  earth  to  a  depth  of  one  mile. 
Under  unfavorable  conditions  they  stop 
dividing  and  form  spores,  in  which  state 
they  remain  until  conditions  of  temperature 
and  moisture  are  such  that  growth  may 
begin  again. 


Bacteria,  highly  magnified; 
a,  the  germ  of  typhoid 
fever,  stained  to  show 
the  cilia;  6,  a  spiral 
ciliated  form;  c,  a  rod- 
shaped  form,  in  chains; 
d,  a  spherical  form. — 
a,  b,  from  Engler  and 
Prantl. 


Method  of  Study.  —  Bacteria  can  be  studied 
only  with  the  aid  of  the  microscope.  In  order  to 
get  a  number  of  bacteria  of  a  given  kind  to  study, 
it  becomes  necessary  to  grow  them  in  what  is 
known  as  a  pure  culture.  This  is  done  by  first 
growing  the  bacteria  in  some  medium  such  as  beef 
broth,  gelatin,  or  on  potato.^  The  material  used 
as  a  growth  medium  is  at  first  sterilized  by  heating 
to    such    a   temperature   as  to    kill    all    life    that 

might  be  there.  Now  expose  the  material  to  the  air  of  the  schoolroom  in 
a  shallow  dish  (known  as  a  Petri  di.sh)  or  a  test  tube  in  the  case  of  beef 
broth,  for  say  five  minutes.  Then  cover  the  dish  or  tube  and  put  it  away 
in  a  warm  place  for  a  day  or  two.  Little  spots  appear  on  the  surface  of 
the  gelatin  or  potato,  or  the  beef  broth  becomes  cloudy. 

Pure  Culture.  —  The  spots  are  colonies  composed  of  millions  of  bacteria. 
If  now  we  wish  to  study  one  given  form,  it  becomes  necessary  to  isolate 
them  from  the  others  on  the  plate.  This  is  done  by  the  following  process: 
A  platinum  needle  is  first  passed  through  a  flame  to  sterilize  it,  that  is,  to 
kill  all  living  things  that  may  be  on  the  needle  point.  Then  the  needle  is 
dipped  in  a  colony  containing  the  bacteria  we  wish  to  study.  This  mass  of 
bacteria  is  quickly  transferred  to  another  sterilized  plate,  and  this  plate  is 
immediately  covered  to  prevent  any  other  forms  of  bacteria  from  entering. 
When  we  have  succeeded  in  isolating  the  kind  of  bacteria  in  a  given  dish,  we 
are  said  to  have  a  pure  culture. 

Fermentation.  — -  Bacteria  play  an  important  part  in  the 
process  of    fermentation.     For  example,  bacteria    act  upon  the 

^  For  directions  for  making  a  culture  medium,  see  Peabody,  Manunl  of  Phi/.<^i- 
ology. 


170 


BOTANY 


alcohol  in  cider,  and  by  a  chemical  process  change  the  alcohol  to 
vinegar.  Others,  called  the  lactic  acid  bacteria,  bring  about  the 
souring  of  milk  by  acting  on  the  sugar  found  in  the  milk.  Thus 
they  aid  in  butter  and  cheese  making.  Others  give  the  flavor  to 
cheese  or  butter.  Some  are  of  great  economic  importance,  as  we 
have  already  seen,  in  their  relation  to  the  roots  of  some  plants, 
where  they  fix  nitrogen  in  such  a  form  that  it  can  be  used  by 
the  plants  as  food.  Bacteria  seem  to  prefer  to  feed  upon  sub- 
stances that  contain  nitrogen,  this  element  being  necessary  to 


Microscopic  appearance  of  ordinary  milk  showing  fat  globules  and  bacteria.    The  cluster  of 
bacteria  on  left  side  are  lactioracid-forming  germs.    (H.  L.  Russell,  Wis.  Bui.  No.  62.) 

form  protoplasm.  They  are  found  in  great  numbers  upon  all 
nitrogenous  foods,  as  milk,  meats,  fish,  etc.  Feeding  upon  such 
substances,  they  decompose  them  and  cause  decay  to  take  place. 
Typhoid.  —  Such  bacteria  as  are  parasitic  in  the  human  body 
may  cause  disease.  Sometimes  the  harm  is  done  by  certain  poisons 
called  ptomaines,  which  are  formed  by  the  bacteria  during  the 
process  of  growth.  The  disease  we  call  typhoid  fever  is  thus 
caused.  The  bacterium  causing  the  fever  is  taken  into  the  body 
through  the  mouth  in  water,  milk,  or  other  food.  Once  in  the 
intestine  the  bacteria  multiply  very  rapidly,  producing  a  ptomaine. 
This  poison  gets  into  the  blood  and  is  passed  to  all  parts  of  the 


FLOWERLESS   PLANTS  171 

body,  causing  the  symptoms  of  the  disease  we  call  typhoid.  To 
prevent  the  spread  of  this  disease,  we  must  guard  our  water  and 
milk  supply  most  carefully,  in  order  to  prevent  any  of  the  bacteria 
which  cause  the  disease  from  gaining  entrance  into  the  body. 

Tetanus  or  Blood  Poisoning.  —  The  bacterium  causing  blood 
poisoning  is  another  ptomaine-forming  germ.  It  lives  in  the 
earth  and  enters  the  body  by  means  of  cuts  or  bruises.  It  seems 
to  thrive  best  in  less  oxygen  than  is  found  in  the  air.  It  is  there- 
fore important  not  to  close  up  with  court  plaster  wounds  in  which 
such  germs  may  have  found  lodgment.  It,  with  typhoid,  is 
responsible  for  four  times  as  many  deaths  as  bullets  and  shells  in 
time  of  battle.  The  wonderfully  small  death  rate  of  the  Japanese 
army  in  their  war  with  Russia  was  due  to  the  fact  that  the  Jap- 
anese soldiers  always  boiled  their  drinking  water  before  using  it, 
and  their  surgeons  always  dressed  all  wounds  on  the  battle 
field,  using  powerful  antiseptics  in  order  to  kill  any  bacteria 
that  might  find  lodgment  in  the  exposed  wounds. 

Tuberculosis.  —  Another  bacterium  that  is  responsible  for  nearly 
one  seventh  of  all  the  yearly  deaths  in  the  world  is  the  so-called  tu- 
bercle bacillus.  It  causes  the  disease  called  tuberculosis.  This  disease 
is  not  caused  by  a  ptomaine,  but  by  the  growth  of  the  bacteria 
in  the  lungs,  and  other  parts  of  the  body,  where  they  eat  away  the 
tissues  of  the  lungs  and  form  little  masses  of  new  tissue,  called 
tubercles.  Tuberculosis  may  be  contracted  by  taking  the  bacteria 
into  the  throat  or  lungs  in  the  air  we  breathe.  Although  there 
are  always  some  of  the  germs  in  the  air  of  an  ordinary  city  street, 
and  though  we  doubtless  take  some  of  these  germs  into  our 
bodies  every  day,  yet  the  bacteria  seem  able  to  gain  a  foothold 
only  under  certain  conditions.  It  is  only  when  the  tissues  are 
in  a  worn-out  condition,  when  we  are  ''  run  down,"  as  we  say,  that 
the  parasite  may  obtain  a  foothold  in  the  lungs.  Even  if  the 
disease  gets  a  foothold,  it  is  quite  possible  to  cure  it  if  it  is  taken 
in  time.  The  germ  of  tuberculosis  is  killed  by  exposure  to  bright 
sunlight  and  fresh  air.  Thus  the  course  of  the  disease  may  be 
arrested,  and  a  permanent  cure  brought  about,  by  a  life  in  the 
open  air,  the  patient  sleeping  out  of  doors,  taking  plenty  of  nour- 
ishing food  and  moderate  exercise. 


172 


BOTANY 


Many  other  diseases  have  been  traced  to  bacteria.  Diphtheria 
and  asiatic  cholera  are  tlie  best  known.  Grippe,  pneumonia, 
whooping  cough,  and  colds  are  believed  to  be  caused  by  bacteria. 
Other  diseases,  as  malaria,  yellow  fever,  and  probably  smallpox, 
scarlet  fever,  and  measles,  are  due  to  the  presence  in  the  blood  of 
a  one-celled  animal  parasite. 

Methods  of  Fighting  Germ  Diseases.  —  As  we  have  seen,  dis- 
eases produced  by  bacteria  may  be  caused  by  the  bacteria  being 
transferred  from  one  person  directly  to  another,  or  the  disease 
may  obtain  a  foothold  in  the  body  in  food,  or  water,  by  breath- 
ing in  the  germs  in  the  air,  or  by  taking  them  into  the  blood 
through  a  cut  or  wound. 

In  the  prevention  of  germ  diseases  we  must  fight  the  germ 
by  attacking  the  parasites  directly  with  poisons  that  will  kill 
them  (such  poisons  are  called  germicides  or  disinfectants),  and 
we  must  strive  to  make  the  persons  coming  in  contact  with  the 
disease  unlikely  to  take  the  disease.  This  insusceptibility  or 
immunity  may  be  either  natural  or  acquired.  Immunity  may  be 
acquired  by  means  of  such  treatment  as  the  anti-toxin  treatment  for 
diphtheria.  This  treatment,  as  the  name  denotes,  is  a  method  of 
neutralizing  the  poison  {toxin)  caused  by  the  bacteria  in  the  system. 
It  was  discovered  a  few  years  ago  that  the  serum  of  the  blood  of 

an  animal  immune  to  diphtheria  is 
capable  of  neutralizing  the  poison  pro- 
duced by  the  diphtheria-causing  bac- 
teria. Horses  are  rendered  immune  by 
giving  them  large  doses  of  the  diph- 
theria toxin  or  poison.  The  serum  of 
the  blood  of  these  horses  is  then  used 
to  inoculate  the  patient  suffering  from 
or  exposed  to  diphtheria,  and  thus  the 
disease  is  checked  or  prevented  alto- 
gether. 


A  lichen  {Physcia  stellaris); 
a,  spore-bearing  organs. 


Lichens.  —  Lichens  may  be  found  incrust- 
ing  rocks,  tree  trunks,  or  other  exposed  locali- 
ties. They  have  in  general  a  grayish  color,  although  they  may  be  red, 
yellow,  or  black.     The  form  of  the  body  is  usually  that  of  a  thallus,  being 


FLOWERLESS   PLANTS 


173 


Stages  in  the  formation  of  the 
lichen  thallus,  showing  the  rela- 
tion of  the  threadlike  fungus  to 
the  green  cells  of  the  alga.  After 
Bornet. 


flat  and  irregular.  One  of  the  commonest  of  the  lichens  (P/i?/scta),  found 
on  stone  walls  or  tree  trunks,  produces  cup-shaped  bodies  from  the  thallus, 
in  which  spores  are  formed.  Most  lichens 
have  definite  spore-producing  structures 
which  protrude  from  the  upper  surface  of 
the  thallus.  A  lichen  is  of  interest  to  us 
chiefly  because  it  shows  a  partnership  to 
exist  between  certain  green  plants,  called 
the  algse,  and  the  fungi.  A  lichen  is  thus 
composed  of  two  plants,  one  at  least  of 
which    may    live  alone,   but   which    have 

formed  a  partnership  for  life,  and  have  divided  the  duties  of  such  life  be- 
tween them.  In  most  lichens  the  alga,  a  green  plant,  forms  starch  and 
nourishes  the  fungus.  The  fungus,  in  turn,  produces  spores,  by  means  of 
which  new  lichens  are  started  in  life.  The  body  of  the  lichen  is  usually  pro- 
tected by  the  fungus,  which  is  stronger  in  structure  than  the  green  part 
of  the  combination.  This  process  of  living  together  for  mutual  advantage  is 
called  symbiosis.  Some  animals  thus  combine  with  plants;  for  example, 
the  tiny  animal  known  as  the  hydra  with  certain  of  the  one-celled  algae. 
Animals  also  frequently  live  in  this  relation  to  each  other. 

Algae.  —  The  algse  are  a  very  diverse  collection  of  plants,  con- 
taining some  of  the  smallest  and  simplest  as  well  as  some  of  the 

largest  plants  in  the  world. 
The  tiny  one-celled  Pleuro- 
coccus  is  an  example  of  the 
former;  the  giant  kelps  of 
the  Pacific  Ocean,  which  at- 
tain a  length  of  over  one 
thousand  feet,  of  the  latter. 
The  body  of  the  algse  is  a 
thallus,  which  may  be  plate- 
like, circular,  ribbon-formed, 
threadlike,  or  filamentous. 
It  may  even  be  composed  of 
a  single  cell.  A  large  num- 
ber of  the  algse  inhaliit  the 
water,  either  fresh  or  salt. 
In  color  they  vary  from  green  through  the  shades  of  blue-green  to 
yellow,  brown,  and  red.  These  colors  are  best  seen  in  the  sea- 
weeds,  all  of   which,  however,  contain  chlorophyll.     In  the  red 


A  red  seaweed,  showing  a  finely  divided 
thallus  body. 


174 


BOTANY 


and  brown  seaweeds  the  chlorophyll  is  concealed  by  other  coloring 
material  in  the  plant  body.  In  the  olive-brown  fucus  (the  com- 
mon rockweed)  it  is  easy  to  prove  the  presence  of  chlorophyll  by 
cutting  open  the  bladders  which  are  found  in  the  plant  body. 
Chlorophyll  may  also  be  extracted  by  placing  the  plant  in  alcohol. 
The  red  seaweeds  are  among  the  most  beautiful  and  delicate  of 


Rockweed,  a  brown  alga,  showing  the  distribution  on  rocks  below  highwater  mark. 

all  plants.     They  may  be  mounted  under  water  upon  cardboard 
and  then  studied  after  dryang.^ 

Green  Algae.  —  The  collection  of  plants  known  as  the  green 
algae  are  of  more  interest  to  us  because  of  their  distribution  in 
the  fresh  waters  of  New  York  state,  and  also  because  of  their 
economic  importance  as  a  supply  of  oxygen  for  fish  and  other  ani- 
mals in  the  waters  of  our  inland  lakes  and  rivers.  Our  atten- 
tion is  called  to  them  in  an  unpleasant  way  at  times,  when,  after 
multiplying  very  rapidly  during  the  hot  summer,  they  die  rapidly 

*  For  the  study  of  a  seaweed,  see  Hunter  and  Valentine,  Manual,  pa^c  81.  For 
reference  reading,  see  Bergen  and  Davis,  Principles  of  Bolany,  page  172 


FLOWERLESS   PLANTS 


175 


and  leave  their  remains  in  our  water  supply.  Much  of  the  un- 
pleasant taste  and  odor  of  drinking  water  comes  from  this  cause. 
Pond  Scum  (Spirog7jra) .— This  alga  is  well  known  to  every 
boy  or  girl  who  has  ever  seen  a  small  pond  or  sluggish  stream.  It 
grows  as  a  slimy 
mass  of  green 
threads  or  fila- 
ments. Frequent- 
ly it  is  so  plentiful 
as  almost  to  cover 
the  surface  of  the 
water,  buoyed  up 
by  little  bubbles 
of  a  gas  which 
seems  to  arise  from 
the  body  of  the 
plant.  If  we  place 
some  of  the  Spiro- 
gyra  in  a  deep  dish 
of  water,  taking 
care  to  put  the 
dish  in  the  sun, 
the  green  plant  will  be  found  to  give  off  enough  gas  to  cause  the 
plants  to  float  near  the  surface.  If  we  collect  some  of  this  gas, 
we  can  easily  prove  that  it  is  oxygen.  The  person  who  sees  a 
pond  with  a  covering  of  slimy  pond  scum,  knowing  this  fact, 
should  no  longer  feel  that  the  pond  is  a  menace  to  health,  un- 
less, indeed,  it  is  a  place  where  mosquitoes  live  and  breed. 

n 


^                    1 

I^^^^^^^^^^H 

a 

■ 

p.: 

A 


B 


A ,  jar  of  water  containing  pond  scum;  B,  same  jar  after  an 
hour  in  the  sunlight. 


Spirogyra:  n,  nucleus;  s,  chlorophyll  bands. 


Suggestions  for  Observational  Work}  —  Under  the  low  power  of  the  micro- 
scope, try  to  make  out  the  length  of  one  of  the  filaments  of  Spirogyra.     Do 

*  For  fvdler  directions,  see  Hunter  and  Valentine.  Manual,  page  79. 


176 


BOTANY 


the  filaments  branch  ?  Are  they  fastened  at  one  end  ?  A  filament  is  com- 
posed of  a  number  of  cells  placed  end  to  end.  Notice  a  single  cell  rather 
carefully  with  the  low  power  first,  and  then  under  the  high  power.  The 
following  structures  can  be  made  out  by  the  careful  observer :  — 

(a)  The  cell  wall. 

(b)  The  chlorophyll  bands.     Determine  if  there  is  one  or  more  in  a 
single  cell.     The  number  varies  in  different  species. 

(c)  The  colorless  protoplasm ;  this  is  usually  best  seen  close  to  the  cell 
wall. 

(d)  The  nucleus,  suspended  in  the  middle  of  the  cell  by  strands  of  proto- 
plasm. 

Draw  a  single  cell  as  you  see  it  under  the  high  power  of  the  microscope, 
and  label  each  part  mentioned  above. 

Pond  scum  may  grow  by  a  simple  division  of  the  cells  in  a 
filament.  Another  method  of  reproduction  is  seen  in  this  plant. 
The  cells  of  two  adjoining  filaments  may  push  out  tubes  which 

meet,  thus  connecting  the  cells  of  two  different 
filaments  with  each  other.  Meantime  the  proto- 
plasm of  the  cells  thus  joined  condenses  into  two 
tiny  spheres;  the  bands  of  chlorophyll  are  broken 
down,  and  ultimately  the  contents  of  one  of  the 
cells  passes  over  tho  tube  and  mingles  with  the  cell 
of  the  neighboring  filament,  with  which  it  was  pre- 
viously connected  by  the  tube  formed  from  the 
cell  walls.  As  in  black  mold,  the  result  of  this 
process  of  fusion  is  a  thick-walled  resting  cell  which 
we  call  a  zygospore.  This  cell  can  withstand  con- 
siderable extremes  of  heat  and  cold,  and  may  be 
dried  to  such  an  extent  that  it  is  found  in  dust  or 
C^  in  the  air.     Under  favorable  conditions,  this  spore 

'       '    '  will  germinate  and  produce  a  filament. 

Conjugation.  —  The  process  in  which  two  cells  of 
equal  size  unite  to  form  a  single  cell  is  called  conju- 
gation.    It  is  believed  to  be  a  sexual  process  which 
corresponds  in  a  way  to   the  fertilization  in  the 
If  material  is  obtainable,  draw  several  stages  in 


Conjugation  of 
Spirogyra;  zs, 
zygospore;  /, 
fusion  in  prog- 
ress. 


higher  plants. 

the  process  of  conjugation.^ 

^  Material  which  shows  conjugation  is  not  always  easy  to  obtain.  Conjugation 
usually  takes  place  most  freely  in  the  fall  of  the  year.  When  material  is  obtained 
it  may  be  preserved  in  a  4  per  cent  solution  of  formol.  Material  killed  in  a  5  per 
cent  solution  of  chromic  acid  and  then  preserved  in  70  per  cent  alcohol  or  4  per  cent 
formol  shows  the  details  of  cellular  structure. 


FLOWERLESS  PLANTS 


177 


Pleurococcus.  —  The  simplest  of  all  green  plants  are  the  one-celled  algae. 
One  of  the  commonest  forms  is  the  plant  called  Pleurococcus,  which  is 
found  in  vast  numbers  on  the  bark  of  trees,  on  moist  fence  posts,  on  the 
shaded  parts  of  buildings  and  other  moist  localities.* 

If  we  gently  scrape  some  of  the  green  material  from  a  bit  of  bark  con- 
taining these  plants  into  a  shallow  dish  containing  water,  and  after  a  few 
minutes  transfer  some  of  the  material  to  a  glass  slide  and  examine  it  under 
the  high  power  of  the  microscope,  something  of  the  structure  of  the  tiny- 
plants  can  be  made  out. 

Plant  Body.  —  The  plant  body  of  the  Pleurococcus  is  found  to  crnsist 
of  a  single  very  small  green  cell.  This  is  surrounded  by  a  rather  prfjminent 
wall  of  cellulose  or  woody  material.  Notice  the  protoplasmic  contents  of 
the  cell.  Is  the  chlorophyll  arranged  in  a  definite  manner  as  in  the  cell  of 
Spirogyra  ?  Notice  that  many  of  the  cells  are 
joined  together  to  form  colonies.  How  many 
cells  do  you  find  in  such  a  colony?  Do  the 
number  of  cells  thus  grouped  together  differ  ? 
Draw  several  colonies  in  different  stages.  In 
such  a  simple  plant  as  the  Pleurococcus  we 
find  no  other  method  of  reproduction  plainly 
seen  except  that  by  simple  division.  This  _,, 
is  an  asexual  method  known  as  vegetative       ^^^^^fo'n'y'T^ou^r'clSrmei  bl; 

reproduction.  division  of  the  original  cell,  A. 


Formation  OF  Zoospores. — Under  some  circumstances,  however,  certain 
species  of  Pleurococcus  are  known  to  give  rise  to  a  cell  which  is  capable  of 
movement  in  water  by  means  of  two  whiplash  threads  of  protoplasm  which 
protrude  from  one  end  of  the  cell.  This  motile  cell  is  called  a  zoospore 
(animal  spore).  It  does  resemble  a  very  simple  animal  at  this  stage 
of  its  existence.  The  spore  thus  formed  is  an  asexual  spore  which  may 
swim  away  from  the  parent  plant  and  found  colonies  in  a  new  locality. 


Diatoms.  —  These  plants  are  found  in  vast  numbers  living  on  the  mud 
or  stones  at  the  bottom  of  small  streams.  The  plant  body  is  inclosed  in 
a  cell  wall  composed  largely  of  silica 
or  glass.  Many  of  the  diatoms  are 
free-swimming.  They  compose  a 
large  percentage  of  the  living  organ- 
isms found  near  the  ocean's  surface. 
The  plant  body  is  inclosed  by  cell 
walls  composed  of  two  valves  which 
fit  into  each  other  like  a  box  and 
its  cover.     The  cell  color  is  brown. 

Diatoms  are  found  as  fossils,  and 
make  up  a  large  proportion  of  many  rocks.  The  silicious  skeletons  in  such 
rocks  are  made  of  commercial  importance,  the  rock  forming  a  basis  for 
polishing  powders. 

1  See  Hunter  and  Valentine,  Manwd,  page  77. 
hunter's  BIOL. — 12 


Diatoms. 


17S  BOTANY 


Reference  Books 
for  the  pupil 

Andrews,  Botany  All  the  Year  Round,  Chap.  X,     American  Book  Company. 
Atkinson,  Lessons  in  Botany,  Chaps.  Ill,  XIX-XXIX. 
Coulter,  Plant  Studies,  XVII,  XXIV.     D.  Appleton  and  Company. 
Conn,  Bacteria,  Yeasts,  and  Molds  in  the  Home.     Ginn  and  Company. 
How  to  grow  Mushrooms.     Bui.  No.  53,  U.S.  Department  of  Agriculture. 
Mushroom  Poisoning.     Cir.  No.  13,  U.S.  Department  of  Agriculture. 
Parsons,  How  to  know  the  Ferns.     Charles  Scribner's  Sons. 
Prudden,  Dust  and  its  Dangers.     G.  P.  Putnam's  Sons. 
Prudden,  Story  of  the  Bacteria.     G.  P.  Putnam's  Sons. 

FOR    THE    TEACHER 

Goodale,  Physiological  Botany.     American  Book  Company. 

Leavitt,  Outlines  of  Botany.     American  Book  Company. 

Atkinson,  Mushrooms,  Edible  and  Poisonous.     Andrews  and  Church. 

Bergen  and  Davis,  Foundations  of  Botany  (Cryptogamic  portion).  Ginn  and 
Company. 

De  Bary,  Comparative  Anatomy  of  Phanerogams  and  Ferns.     Clarendon  Press. 

De  Bary,  Comparative  Morphology  and  Biology  of  the  Fungi,  Mycetozoa  and  Bacteria. 
Clarendon  Press. 

Marshall,  The  Mushroom  Book.     Doubleday,  Page  and  Company. 

Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 

Strasburger,  Noll,  Schenck,  and  Schimper,  A  Text-hook  of  Botany.  The  Macmillan 
Company. 

Ward,  Timber  and  Some  of  its  Diseases,  Chaps.  V,  VI,  VII,  X-XIIl.  The  Mac- 
millan Company. 

Year  Book,  U.S.  Department  of  Agriculture,  1894,  1897,  1900.     Bui.  No.  16. 


PART  II.     ZOOLOGY 

XII.     PROTOZOA 

A  Hay  Infusion.  —  The  smallest  and  simplest  plants  studied 
were  composed  of  a  single  cell;  the  simplest  animals  are  likewise 
composed  of  but  one  cell.  Place  a  wisp  of  hay  or  straw  in  a  small 
glass  jar  nearly  full  of  water,  and  leave  it  for  a  few  days  in  a  warm 
room.  Certain  changes  are  seen  to  take  place  in  the  contents  of 
the  jar;  the  water  after  a  little  gets  cloudy  and  darker  in  color;  a 
scum  appears  on  the  surface,  which  is  made  up  of  bacteria.  These 
bacteria  evidently  aid  in  the  decay  which  (as  the  unpleasant  odor 
from  the  jar  testifies)  is  taking  place.  Later,  small  one-celled 
animals  appear;  these  multiply  with  wonderful  rapidity,  so  that 
in  some  cases  the  surface  of  the  water  seems  to  be  almost  white 
with  active  one-celled  forms  of  life.  If  we  ask  ourselves  where 
these  animals  come  from,  we  are  forced  to  the  conclusion  that 
they  must  have  been  in  the  water,  the  air,  or  the  hay.  Hay  is 
dried  grass,  which  may  have  been  cut  in  a  field  near  a  pool  con- 
taining these  creatures.  When  these  pools  dried  up,  the  wind  may 
have  scattered  some  of  these  little  organisms  in  the  dried  mud  or 
dust.  Some  may  exist  in  a  dormant  state  on  the  hay,  the  water 
serving  to  awaken  them  to  active  life.  In  the  water  too  there 
may  have  been  some  living  cells,  plant  and  animal.  In  the  decay- 
ing hay  and  in  water  are  cell  food  in  abundance,  both  inorganic 
and  organic.  Living  cells  increase  rapidly  here  because  of  the 
favorable  conditions  under  which  they  exist.  This  combination 
of  living  and  dead  matter  just  described  is  called  a  hay  infusion. 

Study  of  the  Paramcecium.}  —  Let  us  now  take  up  the  study  of  one  of  these 
simple  one-celled  animals  found  in  a  hay  infusion.  For  this  purpose  the 
compound  microscope,  slides,  coverslips,  a  little  powdered  carmine,  and  an 
infusion  containing  paramoecia  are  necessary.  Paramoecia  usually  appear  in 
a  hay  infusion  in  three  or  four  days. 

The  form  of  the  paramcecium,  or  slipper  animalcule,  as  it  is  sometimes 
called,  is  elongated,  oval  in  outline,  and  somewhat  flattened.     Notice  that 

^  Hunter  and  Valentine,  Manual,  page  163. 

179 


180 


ZOOLOGY 


one  end  is  slightly  pointed.  This  is  called  the  anterior  end.  Do  the  animals 
always  move  at  the  same  rate  of  speed?  Do  they  ever  turn  over,  or  is  one 
side  always  uppermost?     What  happens  when  they  meet  an  obstruction? 

The  locomotion  of  the  paramoecium  is  caused  by  the  movement  of  a 
number  of  tiny  threads  of  protoplasm,  the  cilia.     These  cilia  lash  the  w'ater 

like  a  multitude  of  tiny  oars.  If  a  little  powdered 
carmine  is  allowed  to  run  under  the  cover  glass,  the 
currents  of  water  caused  by  the  cilia  may  easily  be 
seen. 

Some  of  the  carmine  grains  may  be  found  later 
inside  the  body  of  the  paramoecium.  Notice  carefully 
the  direction  taken  by  the  currents  of  w^ater  bearing 
the  carmine  grains  (or  food  particles),  and  try  to 
locate  a  funnel-like  opening.  At  the  bottom  of  this 
funnel  is  the  mouth. 

You  will  notice  that  the  particles  of  carmine  (or 
food  materials)  are  gathered  into  little  balls  within  the 
almost  transparent  protoplasm  of  the  cell.  These 
masses  of  food  seem  to  be  inclosed  within  a  little  area, 
containing  fluid,  called  a  vacuole.  Other  vacuoles  ap- 
pear to  be  clear;  these  are  spaces  in  which  food  has 
been  digested.  One  or  tw^o  other  larger  vacuoles  may 
sometimes  be  found,  these  are  the  contractile  vacuoles; 
their  purpose  seems  to  be  to  pass  off  waste  material 
from  the  cell  body.  This  is  done  by  pulsation  of  the 
vacuole,  which  ultimately  bursts,  passing  out  fluid  waste 
to  the  outside.  Solid  w'astes  are  passed  out  of  the  cell 
in  somewhat  the  same  manner.  The  nucleus  of  the 
cell  is  not  visiole  in  living  specimens.  In  a  cell  that 
has  been  stained  it  has  been  found  to  be  a  double 
structure,  consisting  of  one  large  and  one  small  portion. 
Make  a  drawing  of  a  paramoecium,  showing  as  many 
of  the  above-mentioned  parts  as  you  can  find. 


Paramoecium.  Greatly 
magnified.  From 
side.  F.V.,  food 
vacuole;  C.V.,  con- 
tractile vacuole;  M, 
mouth;  N ,  nucleus; 
W  F.,  water  vacuole. 
(After  Sedgwick  and 
Wilson.) 


Response  to  Stimuli.  —  In  the  paramoecium,  as  in  the  one-celled 
plants,  the  protoplasm  composing  the  cell  can  do  certain  things. 
Protoplasm  responds,  in  both  plants  and  animals,  to  certain  agen- 
cies acting  upon  it,  coming  from  without;  these  agencies  we  call 
stimuli.  Such  stimuli  may  be  light,  differences  of  temperature, 
presence  of  food,  electricity,  or  other  factors  of  its  surroundings. 
Plant  and  animal  cells  may  react  differently  to  the  same  stimuli. 
In  general,  however,  we  know  that  protoplasm  is  irritable  by  some 
of  these  factors.  To  severe  stimuli,  protoplasm  usually  responds 
by  contracting,  another  power  which  it  possesses.  We  know,  too, 
that  plant  and  animal  cells  take  in  food  and  change  the  food  to 
protoplasm,  that  they  breathe,  that  they  may  waste  away  and 
repair  themselves,  and  that  new  plant  and  animal  cells  are  repro- 
duced from  the  original  bit  of  protoplasm,  a  single  cell. 


PROTOZOA 


181 


Reproduction  of  Paramcecium.  —  Somctimos  a  paramoecium  may  be 

found  in  the  act  of  dividing  by  the  process  known  as  fission,  to  form  two 

new  cells,  each  of  which  contains  half  of  the  oiigi- 
nal  cell.  This  is  a  method  of  asexual  reproduc- 
tion. 

Frequently  another  method  of  reproduction  may 
be  observed.  This  is  called  conjugation  and  some- 
what resembles  the  same  process  in  the  thallo- 
phytes.  Two  cells  of  equal  size  attach  themselves 
as  shown  below,  complicated  changes  take  place  in 
the  nuclei  of  the  two  cells  thus  united,  and  after  a 
short  period  of  rest  the 
two  cells  separate  as  two 
new  individuals.  These 
new  animals  appear  to  be 
rejuvenated  as  a  result  of 

conjugation,  and  may  continue  to  reproduce  asexU' 

ally  by  fission  for  a  long  period  of  time.     Even- 

ually,  howeve--,  it  seems  necessary  for  the  cells  to 

conjugate  in  order  to  continue  their  existence.     This 

stage  of  conjugation  we  believe  in  the  plants  to  be 

a   sexual    stage.      There    seems    every    reason    to 

believe  that  it  is  a  like  stage  in  the  life  history  of 

the  paramoecium. 


NAC. 
M/C. 


Paramoecium  dividing  by 
fission.  Greatly  magni- 
fied. M,  mouth;  MAC, 
macronucleus;  MIC, 
micronucleus.  (After 
Sedgwick  and  Wilson.) 


maQ 


Paramoecium  conjugating. 
Greatly  magnifietl.  M, 
mouth  ;  Mic  ,  micro- 
nucleus;  Mac,  macro- 
nucleus;  CF.,  contrac- 
tile vacuole.  (.\fter 
Sedgwick  and  Wilson.) 


Amoeba.  —  In  order  to  understand  more  fully  the  life  of  a 
simple  bit  of  protoplasm,  let  us  take  up  the  study  of  the  amoeba, 
a  type  of  the  simplest  form  of  life  known,  either  plant  or  animal. 
Amoeba  may  be  obtained  from  the  dead  leaves  in  the  bottom 
of  small  pools,  from  the  same  source  in  fresh-water  aquaria, 
from  the  roots  of  duckweed  or  other  small  water  plants,  or  from 
green  algae  growing  in  quiet  localities.  No  sure  method  of  obtain- 
ing them  can  be  given.  Unlike  the  plant  and  animal  cells  we 
have  examined,  the  amoeba  has  no  fixed  form.  Viewed  under  the 
compound  microscope,  it  has  the  appearance  of  an  irregular  mass 
of  granular  protoplasm.  Its  form  is  constantly  changing  as  it 
moves  about.  This  is  due  to  the  pushing  out  of  tiny  projections 
of  the  protoplasm  of  the  cell,  called  pseudopodia  (false  feet).  The 
outer  layer  of  protoplasm  is  not  so  granular  as  the  inner  part; 
this  outer  layer  is  called  ectoplasm,  the  inside  being  called 
endoplasm.     In  the  central  part  of  the  cell  is  the  nucleus.     This 


182 


ZOOLOGY 


Amtpba,  with  pseudopodia  (P) 
extended;  EC,  ectoplasm; 
END.,  endoplasm;  the  dark 
area  (A'')  is  the  nucleus.  From 
photograph  loaned  by  Prof.  G. 
N.  Calkins. 


important  organ  is  difficult  to  see  ex- 
cept in  cells  that  have  been  stained. 

The  locomotion  is  accomplished,  ac- 
cording to  Professor  Jennings  of  the 
University  of  Pennsylvania,  by  a  kind 
of  rolling  motion, "  the  upper  and  lower 
surfaces  constantly  interchanging  posi- 
tions." The  pseudopodia  are  pushed  for- 
ward in  the  direction  which  the  animal 
is  to  go,  the  rest  of  the  body  following. 
Although  but  a  single  cell,  still  the 
amoeba  appears  to  be  aware  of  the  ex- 
istence of  food  when  food  is  near  at 
hand.  Food  may  be  taken  into  the 
body  At  any  point,  the  semifluid  protoplasm  simply  rolling  over 
and  ingulfing  the  food  material.  Within  the  body,  as  in  the 
paramcecium,  the  food  is  inclosed  within  a  fluid  space  or  vacu- 
ole. The  protoplasm  has  the 
power  to  take  out  such  mate- 
rial as  it  can  use  to  form  new 
protoplasm  or  give  energy. 
It  will  then  rid  itself  of  any 
material  that  it  cannot  use. 
Thus  it  has  the  power  of  se- 
lective absorption,  a  charac- 
ter found  in  the  protoplasm 
of  plants  previously  studied. 
The  cell  absorbs  oxygen 
from  the  water  by  osmosis 
through  its  membrane,  giving 
up  carbon  dioxide  in  return. 
Thus  the  cell  breathes. 

Waste  products  formed 
from  the  oxidations .  which 
take  place  in  the  cell  are 
passed  out  by  means  of  the 
contractile  vacuole. 


Amoeba,  showing  the  changes  which  take  place 
during  division.  The  dark  body  in  each  fig- 
ure is  the  nucleus;  the  transparent  circle, 
the  contractile  vacuole;  the  outer,  clear  por- 
tion of  the  body  the  ectoplasm ;  the  granular 
portion,  the  endoplasm;  the  granular  masses, 
food  vacuoles.     Much  magnified. 


PROTOZOA 


183 


The  amoeba,  like  other  one-celled  organisms,  reproduces  by  the 
process  of  fission.  A  single  cell  divides  by  splitting  into  two 
others,  each  of  which  resembles  the  parent  cell  except  that  they 
are  of  less  bulk.  When  these  become  the  size  of  the  parent 
amoeba,  they  in  turn  each  divide.  This  is  a  kind  of  asexual  repro- 
duction. 

When  conditions  unfavorable  for  life  come,  the  amoeba,  like 
some  one-celled  plants,  encysts  itself  within  a  membranous  wall. 
In  this  condition  it  may  become  dried  and  be  blown  through  the 
air.  Upon  return  to  a  favorable  environment  it  begins  life  again 
as  before. 

From  the  study  of  the  amoebahke  organisms  which  are  known  to  cause 
malaria  and  by  comparison  with  the  amcebae  which  Hve  in  our  ponds  and 
swamps,  it  seems  Hkely  that  every  amoeba  has  a  compHcated  hfe  history 
during  which  it  passes  through  a  sexual  stage  of  existence.  Such  a  stage  is 
seen  in  the  conjugation  of  the  paramoecium. 

The  Cell  as  a  Unit.  —  In  the  daily  life  of  a  one-celled  animal  we 
find  the  single  cell  performing  all  the  activities  which  we  shall 
later  find  the  many-celled  animal  is 
able  to  perform.  In  the  amoeba  no 
definite  parts  of  the  cell  appear  to 
be  set  off  to  perform  certain  func- 
tions; .but  any  part  of  the  cell  can 
take  in  food,  can  abs-orb  oxygen, 
can  change  the  food  into  protoplasm 
and  excrete  the  waste  material.  The 
single  cell  is,  in  fact,  an  organism. 

One-celled  Plants  and  Animals 
Compared.  —  In  our  consideration 
of  the  alg2e  we  found  that  the  sim- 
plest of  all  plants  consists  of  a  single 
cell.  This  cell  might  be  fixed  in  one 
place,  as  the  common  form  of  pleurococcus,  or  it  might  move 
about  by  means  of  cilia  (as  seen  in  the  motile  stage  of  pleurococcus 
and  in  many  other  single  cells  considered  to  be  plants).  While 
single-celled  animals  are  usually  free-swimming,  nevertheless  some 
(especially  parasitic  protozoa)  do  not  move  about.     So  the  power 


Skeleton  of  Radiolariaii.  Highly 
magnified.  From  model  at  Amer- 
ican Museum  of  Natural  History. 


184  ZOOLOGY 

of  movement  is  not  alone  sufficient  to  distinguish  plants  from 
animals.  Both  one-celled  plants  and  animals  require  oxygen  to 
maintain  life,  as  has  been  shown  by  repeated  experiments.  The 
protoplasm  of  which  the  ceil  is  composed  reacts  to  the  same 
stimuli  in  both  plants  and  animals.  The  one  distinction  that 
seems  to  exist  between  a  plant  and  animal  cell  is  that  in  the 
plant  cell  food  is  manufactured  by  means  of  the  chlorophyll  con- 
tained in  it.  Animal  cells  contain  no  chlorophyll  and  require 
organic  food. 

Habitat  of  Protozoa.  —  Protozoa  are  found  almost  everywhere  in 
shallow  water,  seemingly  never  at  any  great  depth.  They  appear  to  be 
attracted  near  to  the  surface  by  light  and  the  supply  of  oxygen.  Every 
fresh-water  lake  swarms  with  them,  the  ocean  contains  countless  myriads 
of  many  different  forms. 

Use  as  Food.  —  They  are  so  numerous  in  lakes,  rivers,  and  the  ocean  as 
to  form  the  food  for  many  animals  higher  in  the  scale  of  Kfe.  Almost  all 
fish  that  do  not  take  the  hook  and  that  travel  in  "  schools,"  or  com- 
panies, migrating  from  one  place  to  another,  live  partly  on  such  food. 
Many  feed  on  slightly  larger  animals,  which  in  turn  eat  the  Protozoa. 
Such  fish  have  on  each  side  of  the  mouth  attached  to  the  gills  a  series  of 
small  structures  looking  like  tiny  rakes.  These  are  called  the  gill  rakers, 
and  are  used  by  the  fish  to  collect  tiny  organisms  out  of  the  water  as  it 
passes  over  the  gills.  The  whale,  the  largest  of  all  mammals,  strains  pro- 
tozoans and  other  small  animals  and  plants  out  of  the  water  by  means  of 
hanging  plates  of  whalebone,  the  slender  filaments  of  which  form  a  sieve 
from  the  top  to  the  bottom  of  the  mouth. 

Skeleton  Building.  —  Some  of  the  Protozoa  build  elaborate  skeletons. 
These  may  be  formed  outside  of  the  body,  being  composed  of  tiny  micro- 
scopic grains  of  sand,  or  other  materials.  In  some  forms  the  skeleton  is 
internal,  and  may  be  made  of  lime  which  the  animals  take  out  of  the  water. 
Still  other  Protozoa  construct  shells  which  house  them  for  a  time;  then, 
growing  larger,  they  add  more  chambers  to  their  shell,  forming  ultimately  a 
covering  of  great  beauty.  These  shells  or  skeletons  of  Protozoa,  falling  to 
the  sea  bottom,  cover  the  ocean  floor  to  a  depth  of  several  feet  in  places. 

The  Protozoa  have  also  played  an  important  part  in  rock  building.  The 
chalk  cliffs  of  England  and  other  chalk  formations  are  made  up  to  a  large 
extent  of  the  tiny  skeletons  of  Protozoa,  called  Foraminifera.  Some  lime- 
stone rocks  are  also  composed  in  large  part  of  such  skeletons. 

Flagellates. —  Some  cells  show  characters  which  are  like  both  plants 
and  animals.  Such  are  the  group  of  organisms  known  as  flagellates.  All 
flagellates  move  through  the  water  by  means  of  one  or  two  (rarely  more) 
Jong  threads  of  protoplasm,  or  cilia.     Some  flagellates  are  provided  with 


PROTOZOA 


185 


Euglena  ;  F,  flagel- 
lurii;  iV,  nucleus; 
Pv,  contractile 
vacuole. 


chlorophyll,  while  others  appear  to  take  in  food  in  the  same  manner  as  animal 
cells.  They  have  a  red  pigment  spot  at  one  end  of  the  cell  body.  This  spot 
is  sensitive  to  light,  hence  it  has  been  called  an  eye- 
spot.  A  common  flagellate  is  called  Euglena.  The  green 
color  of  stagnant  pools  is  due  to  the  presence  of  enor- 
mous numbers  of  this  organism  in  the  water. 

Relation  of  Protozoa  to  Disease.  —  The  study  of 
the  life  history  and  habits  of  the  Protozoa  has  resulted  in 
the  finding  of  many  parasitic  forms,  and  the  consequent 
explanation  of  some  kinds  of  disease.  One  parasitic  pro- 
tozoan, like  an  amoeba,  is  called  Plasmodium  malarice.  It 
causes  the  disease  known  as  malaria.  Part  of  its  life  is 
passed  within  the  body  of  a  mosquito  (the  anopheles), 
into  the  stomach  of  which  it  passes  when  the  mosquito 
sucks  the  blood  from  a  person  having  malaria.  Within 
the  body  of  the  mosquito  a  complicated  part  of  the  life 
history  takes  place,  which  results  in  a  stage  of  the  para- 
site establishing  itself  within  the  glands  which  secrete 
the  saliva  of  the  mosquito.  When  the  mosquito  pierces  its  human  prey  a 
second  time,  some  of  the  parasites  are  introduced  into  the  blood  along  with 
the  saliva.  These  parasites  enter  the  corpuscles  of  the  blood,  increase  rap- 
idly in  size,  and  then  form  spores.     The  process  of  spore  formation  results 

in  the  chill  of  malaria.  Later, 
when  the  spores  almost  fill  the 
blood  corpuscle,  it  bursts,  and  the 
parasites  enter  the  blood.  There 
thej^  release  a  poison  which  causes 
the  fever.  The  spores  may  again 
enter  the  blood  corpuscles  and  in 
forty-eight  or  seventy-two  hours 
repeat  the  process  thus  described. 
Another  group  of  piotozoan 
parasites  are  called  trypanosomes. 
One  of  this  family  lives  in  the 
blood  of  native  African  zebras 
and  antelopes;  seemingly  it  does 
them  no  harm.  But  if  one  of 
these  parasites  is  transferred  by 
the  dreaded  tsetse  fly  to  one  of 
the  domesticated  horses  or  cattle 
of  the  colonist  of  that  region, 
death  of  the  animal  results. 
Another  fly  is  believed  to  carry  a  specimen  of  trypanosome  to  the  natives 
of  Central  Africa,  and  to  cause  "  the  dreaded  and  incurable  sleepii-g  sick- 


BIoolI  corpuscles  of  a  patient  with  malarial 
fever.  Two  corpuscles  contain  the  para- 
sites. Photograph,  greatly  enlarged,  by 
Davison, 


186  ZOOLOGY 

ness."     This  disease  carries  off  more  than  fifty  thousand  natives  yearly, 
and  many  Europeans  have  succumbed  to  it. 

Classification  of  Protozoa 

The  following  are  the  principal  classes  of  Protozoa,  examples  of  which  we  have 
seen  or  read  about : 

Class  I.  Rhizopoda  (Gk.  =  root  footed).  Having  no  fixed  form,  with  pseudopodia. 
Either  naked  as  Amoeba  or  building  limy  (Foraminifera)  or  glasslike  skeletons 
(Radiolaria) . 

Class  II.  Infusoria  {in  infusions).  Usually  active  ciliated  Protozoa.  Examples, 
Paramaecium,  Vorticella. 

Class  III.  Sporozoa  (spore  animals).  Usually  parasitic  and  non-active.  Exam- 
ple, Plasmodium  malariee. 

Refehence  Books 

for  the  pupil 

Davison,  Practical  Zoology,  pp.  178-184.     American  Book  Company. 
Herrick,  Text-book  in  General  Zoology,  Chaps.  II,  V.      American  Book  Company. 
Jordan,  Kellogg,  and  Heath.     Animal  Studies,  Chap.  III.     D.  Appleton  and  Com- 
pany. 

FOR   THE   TEACHER 

Dodge,  General  Zoology,  pages  54-65.     American  Book  Company. 

Calkins,  G.  N.,  The  Protozoa.     The  Macmillan  Company. 

Linville  and  Kelly,  General  Zoology,  Chap.  XXI.     Ginn  and  Company. 

Parker.  T.  J.,  Lessons  in  Elementary  Biology.     The  Macmillan  Company. 

Sedgwick  and  Wilson,  General  Biology.     H.  Holt  and  Company, 

Wilson,  E.  B.,  The  Cell  in  Developtnent  and  Inheritance.    The  Macmillan  Company, 


XIII.     METAZOA 


Division  of  Labor.  —  If  we  compare  the  amoeba  and  the  para- 
moecium,  we  find  the  latter  a  more  complex  organism  than  the 
former.  An  amoeba  may  take  in  food  through  any  part  of  the 
body;  the  paramoecium  has  a  definite  gullet;  the  amoeba  may 
use  any  part  of  the  body  for  locomotion;  the  paramoecium  has 
definite  parts  of  the  cell,  the  cilia,  fitted  for  this  work.  Since  the 
structure  of  the  paramoecium  is  more  complex,  we  say  that  it  is  a 
"  higher  "  animal. 

As  we  look  higher  in  the  scale  of  life,  we  invariably  find  that 
certain  parts  of  a  plant  or  animal  are  set  apart  to  do  certain  work 
and  only  that  work.  This  has  resulted  in  what  is  called  division 
of  labor.  Just  as  in  a  community  of  people,  there  are  some  men 
who  do  rough  manual  work,  others  who  are  skilled  workmen, 
some  who  are  shopkeepers,  and  still  others  who  are  professional 
men,  so  among  plants  and 
animals,  wherever  collections 
of  cells  live  together  to  form 
an  organism,  there  is  division 
of  labor. 

One  of  the  simplest  of  all  colo- 
nies is  a  collection  of  cells  called 
Pandorina.  This  is  a  colony  of 
sixteen  cells,  whether  plant  or  ani- 
mal is  uncertain,  which  have  be- 
come joined  by  living  together  in  a 
mass  of  jellylike  material  secreted 
by  the  cells.  They  move  by  means 
of  cilia,  and,  as  a  result  of  living 
together,  move  faster  through  the 
water  and  thus  obtain  more  food 
than  one  alone. 

Another  form  where  division  of  labor  is  begun  is  seen  in  the  plant  (or 
animal)  called  Volvox.     This  is  a  hollow  sphere  of  cells,  the  greater  number 

187 


Colony  of  volvox:  R,  reproductive  cells; 
C,  ciliated  cells.    (After  Kny.) 


188  ZOOLOGY 

of  which  are  ciKated  and  obtain  food  for  the  colony;  a  few,  however,  have 
no  cilia.  These  are  the  reproductive  cells,  which  later  break  away,  and  give 
rise  to  new  colonies  when  the  old  one  dies. 

Protozoa  and  Metazoa.  —  Thus  there  have  come  to  exist  in  the 
animal  world  two  types  of  life :  the  Protozoa,  or  one-celled  indi- 
viduals, and  the  Metazoa,  or  many-celled  animals. 

In  the  Protozoa  the  life  processes  of  growth,  waste  and  repair, 
and  reproduction,  are  carried  on  by  a  single  cell.  In  the  Metazoa 
each  of  these  functions  is  performed  by  collections  of  cells.  In 
the  Metazoa,  too,  division  of  labor  becomes  increasingly  more  per- 
fect as  we  ascend  the  scale  of  complexity  in  form  and  structure 
toward  the  highest  type  of  all,  man. 

Tissues  and  Organs.  —  As  we  have  seen  in  plants,  this  results 
in  a  large  number  of  collections  of  cells  in  the  body,  each  collection 
alike  in  structure  and  performing  the  same  function.  Such  a  col- 
lection of  cells  we  call  a  tissue. 

Frequently  several  tissues  have  certain  functions  to  perform  in 
conjunction  with  one  another.  The  arm  or  leg  of  the  human  body 
performs  movement.  To  do  this,  several  tissues,  as  muscles, 
nerves,  and  bones,  must  act  together.  A  collection  of  tissues  per- 
forming certain  work  is  called  an  organ. 

Tissues  in  the  Human  Body.  —  'Every  animal  body  above  the 
protozoan  is  composed  of  a  certain  number 'of  tissues.  The  cells 
making  up  these  tissues  have  certain  well-defined  characteristics. 
Let  us  see  what  these  cells  may  be,  what  their  structure  is,  and, 
in  a  general  way,  what  function  each  has  in  the  human  body. 

(1)  Muscle  Cells.  —  A  large  part  of  our  body  is  made  up  of 
muscle.  Muscle  cells  are  elongated  in  shape,  and  have  great 
contractile  power.  In  man  they  may  be  of  two  kinds,  voluntary 
(under  control  of  the  will)  and  involuntary. 

(2)  Epithelial  Cells.  —  Such  cells  cover  the  outside  of  a  body 
or  line  the  inside  of  the  cavities  in  the  body.  The  shape  of  such 
cells  varies  from  flat  plates  to  little  cubes  or  columns.  Some 
epithelial  cells  bear  cilia. 

(3)  Connective  Tissue  Cells.  —  Such  cells  form  the  connection 
between  tissues  in  the  body.  They  are  characterized  by  possess- 
ing numerous  long  processes.      They  also  secrete,  as  do  many 


METAZOA 


189 


A,  blood  cell;  5,  a  cili:ited  cell;  C,  a  nerve  cell  showing  axis  cylindei  at  C;  D,  bone-form- 
ing cell ;  E,  a  heart  muscle  cell ;  F,  fibrous  connective  cells. 

other  cellS;  a  substance  like  jelly,  called  intercellular  substance. 
This  stands  in  the  same  relation  to  the  cells  as  does  mortar 
to  the  bricks  in  a  wall. 

Several  other  types  of  cells  might  be  mentioned,  as  blood  cells, 
cartilage  cells,  bone  cells,  and  nerve  cells.  A  glance  at  the  figure 
shows  their  great  variety  of  shapes  and  sizes. 

Functions  Common  to  all  Animals.  —  The  same  functions  per- 
formed by  a  single  cell  are  performed  by  a  many-celled  animal. 
But  in  the  Metazoa  the  various  functions  of  the  single  cell  are 
taken  up  by  the  organs.  In  a  complex  organism,  like  man,  the 
organs  and  the  functions  they  perform  may  be  briefly  given  as 
follows : 

(1)  The  organs  of  food  taking:  mouth  and  parts  which  place 
food  in  the  mouth. 

(2)  The  organs  of  digestion:  the  food  tube  and  the  glands 
connected  with  it.  The  fluids  secreted  by  the  latter  change  the 
foods  from  a  solid  form  (usually  insoluble)  to  that  of  a  fluid.     Such 


190  ZOOLOGY 

fluid  may  then  pass  by  osmosis  through  the  walls  of  the  food 
tube  into  the  blood. 

(3)  The  organs  of  circulation :  the  tubes  through  which  the 
blood,  bearing  its  organic  foods  and  oxygen,  reaches  the  tissues  of 
the  body. 

(4)  The  organs  of  respiration :  the  organs  in  which  the  blood 
receives  oxygen  and  gives  up  carbon  dioxide. 

(5)  The  organs  of  excretion :  such  as  the  kidneys  and  skin,  which 
pass  off  nitrogenous  waste  matter  from  the  body. 

(6)  The  organs  of  locomotion :  muscles  and  their  attachments 
and  connectives,  namely,  tendons,  ligaments,  and  bones. 

(7)  The  organs  of  nerv^ous  control :  the  central  nervous  system, 
which  has  control  of  coordinated  movement. 

(8)  The  sense  organs:  such  as  sight,  hearing,  smell,  taste,  and 
touch. 

Almost  all  animals  have  the  functions  mentioned  above.  In 
most,  the  various  organs  mentioned  are  more  or  less  developed, 
although  in  the  simpler  forms  of  animal  life  some  of  the  organs 
mentioned  above  are  either  very  poorly  developed  or  entirely 
lacking. 

Reference  Rooks 

for  the  pupil 

Herrick,  Text-hook  in  General  Zoology,  Chap.  III.     American  Book  Company. 
Holder,  Half  Hours  rvith  the  Lower  Animals,  Chap.  I.     American  Book  Company. 
French,  Animal  Activities,  Chaps.  Ill,  XI.     Longmans,  Green,  and  Company. 

FOR    THE    TEACHER 

Dodge,  General  Zoology,  Chaps.  VII-X.     American  Book  Company. 
Parker,   Lessons  in  Elementary  Biologij.     The  Macmillan  Company. 
Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 
Verworn,  General  Physiology.     The  Macmillan  Company, 


XIV.     SPONGES 


Limy  Sponge  (Grantia). 

The  sponge  is  the  simplest 
of  all  Metazoa.  One  of 
the  commonest  forms  is 
Grantia,  a  tiny  urn-shaped 
object  found  in  salt  water 
attached  to  piles  or  stones. 
It  is  abundant  in 
Island  Sound. 


Long 


For  this  exercise  have  small 
vials  containing  specimens  of 
Grantia  preserved  in  formol 
or  alcohol.  The  body  is  at- 
tached at  one  end.  What  do 
you  find  at  the  opposite  end  ? 
Label  the  hole  the  osculum. 
This  leads  into  a  cavity  called 
the  cloaca.     The  wall  of  the 


Grantia,  a  limy  sponge,  on  the  shell  of  a  mussel. 
From  photograph  loaned  by  American  Museum  of 
Natural  History. 


body  is  pierced  by  a  number  of  tiny  holes  or  pores 
which  communicate  with  the  cloaca.  The  shape  of 
the  sponge  is  maintained  by  a  skeleton  composed 
of  many  tiny  pieces  or  spicules  of  carbonate  of  lime. 
Notice  the  edge  of  the  osculum.  Make  a  drawing 
of  the  Grantia  twice  natural  size,  showing  all  the 
above  structures.' 

An  examination  with  the  microscope 
shows  the  pores  of  the  sponge  to  be  lined 
with  ciliated  cells.  These,  by  means  of  move- 
ments of  the  cilia,  set  up  a  current  of  water 
toward  the  cloaca.  This  current  bears  food 
particles,  tiny  plants  and  animals,  which  are 
seized  and  digested  by  the  ciliated  cells. 
T^.  r     .     .  These  cells  seemingly  pass  on  the  food  to  the 

Diagram  of  a  simple  sponge;  <=>  ^    i 

t.inhaiant opening;  o, ex-  Other  cells  of  the  body.     The  middle  layer 

halant  opening  or  osciu- 

lum.  1  See  Hunter  and  Valentine,  Manual,  page  159. 

191 


192 


ZOOLOGY 


of  the  body  is  composed  of  structureless  material  containing  cells 
which  secrete  lime  to  form  the  spicules.  Eggs  and  sperms  are 
also  developed  in  this  layer  and  are  set  free  when  ripe  to  develop 
in  the  water. 

Spicules  may  be  freed  from  the  living  part  of  the  sponge  by  placing  a 
Grantia  in  a  strong  solution  of  caustic  soda  for  a  few  minutes.  Mount  a 
little  of  the  sediment  from  the  bottom  of  the  dish  in  water  or  glycerine. 
Note  the  different  forms  of  the  spicules.     Draw  several  for  your  notebook. 

Development  of  the  Sponge.  —  In  the  case  of  the  sponge,  as  in 
most  plants  and  animals,  the  life  history^  begins  with  a  single  cell, 
the  fertilized  egg.  This  cell,  as  we  remember,  has  been  formed  by 
the  union  of  two  other  cells,  a  tiny  (usually  motile)  cell,  the  sperm, 
and  a  large  cell,  the  egg.  After  the  egg  is  fertilized  by  a  sperm 
cell,  it  splits  into  two,  four,  eight,  and  sixteen  cells;  as  the  number 
of  cells  increases,  a  hollow  ball  of  cells  called  the  blastula  is  formed 
(somewhat  like  the  Volvox) ;  later  this  ball  sinks  in  on  one  side 
and  a  double-walled  cup  of  cells,  now  called  a  gastrula,  results. 


#  IP  K  A  #  IK 


Stages  in  the  segmentation  of  an  egg,  showing  the  formation  of  the  gastrula. 

Practically  all  animals  pass  through  the  above  stages  in  their 
development  from  the  egg,  although  these  stages  are  often  not 
plain  to  see  because  of  the  presence  of  food  material  (yolk)  in  the 
egg.  The  gastrula,  which  swims  by  means  of  cilia,  soon  settles 
down,  a  skeleton  is  formed,  other  changes  resulting  in  the  formation 
of  pores  and  osculum  take  place,  and  the  sponge  begins  life  as  an 
adult.  The  early  stages  of  life  when  an  animal  is  unlike  the 
adult  are  known  as  larval  stages;  the  animal  at  this  time  is 
called  a  larva. 

The  young  sponge  consists  of  three  layers  of  cells :  those  of  the 
outside,  developed  from  the  outer  layer  of  the  gastrula,  are  called 


SPONGES 


193 


Here  the  skeleton 
Some  of  the  rarest 


Venus's  flower  basket:  a 
sponge  with  a  glassy  skeleton. 


ectoderm;  the  inner  layer,  developed  from  the  inner  layer  of  the 
gastrula,  the  endoderm.  A  middle  structureless  layer,  called  the 
mesoglea,  is  also  found.  In  higher  animals 
this  layer  (called  mesoderm)  gives  rise  to 
muscles  and  parts  of  other  internal  struc- 
tures. 

Other  Sponges.  —  Sponges  may  be  placed, 
according  to  the  kind  of  skeleton  they  possess, 
in  the  following  groups: 

(1)  The  limy  sponges,  in  which  the  skeleton 
is  composed  of  spicules  of  carbonate  of  lime. 
Grantia  is  an  example. 

(2)  The  glassy  sponges. 
is  made  of  silica  or  glass. 

and  most  beautiful  of  all  sponges  belong  in  this 
class.  The  Venus's  flower  basket  is  the  best 
known. 

(3)  The   horny   fiber    sponges.      These,   the 
sponges  of   commerce,  have  the  skeleton   com- 
posed of  tough  fibers  of  material  somewhat  like 
that  of  cow's  horn.     This  fiber  is  elastic  and  has  the  power  to  absorb  water. 
In  a  hving  state,  the  horny  fiber  sponge  is  a  dark-colored  fleshy  mass, 

usually  found  attached  to  rocks. 
The  warm  waters  of  the  Mediter- 
ranean Sea  and  the  West  Indies 
furnish  most  of  our  sponges.  The 
sponges  are  pulled  up  from  their 
resting  place  on  the  bottom,  either 
by  means  of  long-handled  rakes 
operated  by  men  in  boats,  or  are 
secured  by  divers.  They  are  then 
spread  out  on  the  shore  in  the  sun, 
and  the  living  tissues  allowed  to 
decay;  then  after  treatment  con- 
sisting of  beating,  trimming,  and 
bleaching,  the  bath  sponge  is  ready 
for  the  market. 

Relation  to  Environment. — 
Sponges   are  found  in  both  fresh 
.    ,  „,  r  D    .1,     •         ^,,+      and  salt  water.^     They  are  found 

A    homy    fiber    sponge;     I.P.,   the    mcurrent 

pores;  0,  osculum.    Notice  that  this  sponge  ^  Only  one  species  of  fresh   water 

is  made  up  of  apparently  several  individuals.       sponge,   Spongilla,   is  known   in   this 
One  fourth  natural  size.  country. 

HUNTER^S  BIOL.  — 13 


194  ZOOLOGY 

at  all  depths  and  in  water  of  temperatures  of  varying  degrees.  The 
same  species  of  sponge  in  different  localities  may  assume  very  dififerent 
shapes,  the  immediate  surroundings  acting  upon  the  animal  so  as  to  change 
its  form.  They  appear  to  be  protected  from  fish  and  other  animals  because 
of  their  color  and  form,  their  skeleton,  and  an  unpleasant  odor. 

Reference  Books 

for  the  pupil 

Herrick,  Text-hook  in  General  Zoology,  Chap.  VI.     American  Book  Company. 
Holder,  Half  Hours  with  the  Lower  Animals,  Chap.  II.     American  Book  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies,  Chap.  IV.    D.  Appleton  and  Company. 

FOR    THE    TEACHER 

Miner,  A  Guide  to  the  Sponge  Alcove.     Gmde  Leaflet,  No.  23.     American  Museunc 

of  Natural  History,  New  York. 
Parker  and  Haswell,  Text-book  of  Zoology.     The  Macmillan  Company. 


XV.    CCELENTERATES 


The  Ccelenterata,  —  The  sponge,  as  we  have  seen,  is  an  animal 
of  simple  form  and  of  a  low  order  in  the  scale  of  life.  Another 
simple  animal  is  the  hydra  —  a  type  of  the  group  Ccelenterata. 
The  group  Coelenterata  includes  animals  which  have  a  common 
food  tube  and  body  cavity. 

Hydra.  —  The  common  hydra  lives  in  fresh  water.  It  may  be 
found  living  on  dead  leaves,  submerged  sticks,  stones,  or  weeds  in 
almost  any  fresh-water  pond.  In  a  small  fresh-water  aquarium, 
they  almost  always 
attach  themselves  to 
the  side  of  the  jar, 
where  they  can  be 
watched  and  their 
movements  observed.^ 

Notice    that    when 
contracted    thev    re- 
semble  a  little  whitish 
ball  of   jellylike  sub- 
stance.    When  undis- 
turbed they  elongate 
into  a  hollow  cylinder 
attached  at  one  end. 
A  small  oval  opening 
is  found   at   the  free 
end,  surrounded  with 
a  number  of  little  wav- 
ing arms  called  tenta- 
cles.    Count  them  to  see  how  many  there  are.    If  by  chance  a 
small  water  flea  or  other  crustacean  on  which  the  hydra  feeds 

>  See  Hunter  and  Valentine,  Manual,  page  151. 

195 


Budding  hydra,  as  seen  under  the  low  power  of  a  com- 
pound microscope;  B,  attached  end;  B^,  B^,  buds; 
M,  mouth;  T,  tentacles. 


196 


ZOOLOGY 


happens  near  enough  to  touch  one  of  the  tentacles,  it  is  seen 
to  stop  suddenly  as  if  paralyzed  and  is  then  grasped  by  the 
tentacle  and  carried  toward  the  opening.  The  hydra  is  simply 
a  hollow  bag,  the  digestion  of  the  prey  taking  place  within  it. 
The  waste  products  are  passed  out  through  the  opening  between 
the  tentacles  where  food  is  taken  in. 

The  hydra  may  change  its  position  from  time  to  time.  The  ani- 
mal bends  over,  the  base  is  unfastened,  and  the  animal  "  walks  '^ 
on  its  tentacles  to  a  new  point  of  attachment. 

Structure  of  Body  Wall.  — The  body  wall  of  the  hydra  seen  in  a  cross 
section  is  found  to  be  made  up  of  two  layers  of  cells.  As  in  the  sponge,  the 
inner  layer  serves  for  the  purpose  of  taking  in  and  digesting  the  food.  This 
layer  is  the  endoderm.  The  outer  layer  of  cells  (called  ectoderm)  furnishes 
the  animal  with  weapons  of  offense  and  defense.  This  outer  layer  is  also 
provided  with  cells  which  are  sensitive  (sense  cells).  Between  the  inner  and 
outer  layers  of  cells  is  a  structureless  substance  called  the  mesoglea,  in 
which  are  found  musclelike  fibers,  extensions  of  the  protoplasm  of  the  inner 
outer  layer.  Scattered  among  these  musclelike  fibers  are  some  of  the  cells  of 
the  outer  wall,  irregular  in  shape,  which  have  migrated  in  from  the  outer 
layer.  These  cells  are  the  nerve  cells.  They  furnish  the  animal  with  path- 
ways of  sensation  and  provide  a  means  of  coordinated  movement. 


Organs  of  Offense  and  Detense.  —  If  the  cells  of  the  outer  part 
of  the  tentacle  are  examined  under  the  microscope,  we  find  how 

the  animal  is  able  to  paralyze 
its  prey.  Here  are  found  many 
cells,  the  bodies  of  which  resem- 
ble little  bags.  One  end  of  the 
cell  projects  from  the  outer  sur- 
face of  the  tentacle.  These  cells 
are  the  cnidohlasts,  or  stinging 
cells.  Each  cell  has  in  its  body 
a  small  sac  filled  with  an  acid. 
Attached  to  this  bag  and  rolled 

Stinging    cells    (cnidoblasts);     cnc,  cnidocil;    Up   in  it   is   a    loug   hollow  dart, 

d.,   dart;    n.,   nucleus;    «.,   sac.    (Drawing,    Trrbiph  of\r\   ViP  p-5rr>pllprl  whpn    HiP 
greatly  enlarged,  after  Parker  and  Haswell.)    ^^ICU  CaU   De  expeiieQ  WUeU   tUe 

cell  is  "  set  off."     This  is  done 
by  an  animal  or  substance  brushing  against  a  triggerlike  projec- 


CCELENTERATES 


197 


tion  from  the  cnidoblast.  The  ''  explosion  "  of  the  cell  results  in 
the  ejection  of  the  dart  and  injection  of  the  poisonous  acid  into 
the  victim.  The  animal  hit  by  a  number  of  these  darts  is  usually 
so  paralyzed  that  further  resistance  is  impossible. 

Food  Taking.  —  The  tentacles  then  reach  out  like  arms,  grasp 
the  food,  and  bend  over  with  it  toward  the  mouth.  Digestion 
takes  place  by  means  of  a 
fluid  given  out  from  some 
of  the  cells  near  the  mouth. 
After  the  food  has  been 
partially  digested,  many  of 
the  cells  lining  the  cavity 
put  out  pseudopodia,  which 
grasp  and  ingest  the  food 
particles.  The  tentacles  are 
hollow,  and  the  body  cavity 
extends  into  them.  From 
this  cavit}^  food  may  be 
taken  up  by  cells  in  all  parts 
of  the  body  near  where  it  is 
to  be  used.  The  outer  layer 
of  this  little  animal  does 
not  digest  the  food,  but 
receives  some  of  it  already 
digested    from    the    inner  t      -^  ^-    i     .•      r    u  ^     ^  u  ^  i.     **   u  ^ 

^  Longitudinal  section  of  a  hydra;  b,  bud;  6a,  attached 

layer.  This  food  passes  ^^d;  m,  mouth;  ov,  ovary;  sp,  spermary  holding 
r  „  .  1,  •         1        ,  sperm  cells. 

irom  cell  to  cell,  as  m  plants, 

by  osmosis.  The  oxygen  necessary  to  oxidize  the  food  is  passed 
through  the  body  wall,  seemingly  at  any  point,  for  there  are  no 
organs  for  respiration  (breathing). 

Division  of  Labor.  —  We  have  here  then  a  step  toward  a  more 
complex  animal,  for  certain  parts  of  the  body  here  have  certain 
work  to  perform.  The  outside  for  sensation,  offense  and  defense, 
and  for  movement  and  coordination  of  parts,  and  the  layer  form- 
ing the  interior  of  the  bag  for  taking  in  food,  digesting  it,  and 
distributing  it  to  other  parts  of  the  body. 

Reproduction.  —  The  hydra  reproduces  itself  either  by  budding 


198 


ZOOLOGY 


or  by  the  production  of  new  animals  by  means  of  eggs  and  sperms, 
sexually.  The  bud  appears  on  the  body  as  a  little  knob,  some- 
times more  than  one  coming  out  on  the  same  hydra.  At  first  the 
bud  is  part  of  the  parent  animal,  the  body  cavity  extending  into 
it.  After  a  short  time  (usually  a  few  days)  the  young  hydra 
separates  from  the  old  one  and  begins  life  anew  in  another  place. 
This  is  asexual  reproduction. 

The  hydra  also  reproduces  by  eggs  and  sperms.  These  sperms 
are  collected  in  little  groups  which  usually  appear  near  the  free 
end  of  the  animal,  the  egg  cells  developing  near  the  base  of  the 
same  hydra.  Both  eggs  and  sperms  grow  from  the  middle  layer 
of  the  animal.  The  sperms  when  ripe  are  set  free  in  the  water, 
one  of  them  unites  with  an  egg,  which  is  usually  still  attached  to 
the  body  of  the  hydra,  and  development  begins  which  results  in 
the  growth  of  a  new  hydra  in  a  new  locality. 

Medusa.  —  The  coelenterate  animals  are  a  very  large  group  and 
contain  many  other  animals  than  the  hydra.     All  of  this  group  of 

animals  are  found  in  the 
water,  by  far  the  greatest 
number  of  forms  living  in 
the  ocean.  Among  the 
most  interesting  of  all  the 
coelenterates  inhabiting  the 
salt  water  are  the  jelly  fishes 
or  medusae. 

For  the  study  of  the  Me- 
dusae^ use  Gonionemus  pre- 
served in  formol.  Why  should 
you  call  it  a  "jellyfish"?  Notice 
the  shape  of  the  animal,  some- 
what like  an  umbrella  with  a 
short  handle.  What  do  you 
find  hanging  from  the  edge  of 
the  umbrella?  The  tentacles 
of  the  medusa  are  provided  with  stinging  cells.  Find  and  describe  the  mouth 
at  the  end  of  the  handle  of  the  umbrella  (manubrium).  (N.B.  A  little  car- 
mine or  methylene  blue  dissolved  in  water  may  be  forced  into  the  mouth  of 
the  specimen  with  a  small  medicine  dropper.  This  will  show  clearly  the  di- 
gestive cavity  and  its  canals).  Notice  the  course  taken  by  the  canals  form- 
ing the  digestive  tract.  Hanging  just  under  the  radial  canals  of  the  digestive 
tract  are  found  the  reproductive  bodies,  eggs  or  sperms. 

^  See  Hiinter  and  Valentine,  Manual,  page  156. 


Medusa,  {Gonionemits  murbachii),  showing  tentacles, 
mouth,  digestive  canals,  and  reproductive  bodies. 
Photographed  from  the  model  at  the  American 
Museum  of  Natural  History. 


CGELENTERATES 


199 


Draw  the  medusa  twice  natural  size,  showing  all  the  above  parts  neatly 
labeled. 

Development.  —  The  egg  of  the  medusa  after  fertilization  under- 
goes a  number  of  changes.  First  the  egg  splits  in  two,  then  four, 
eight,  and  ultimately  a  mass  of  cells.  This  process  is  known  as 
segmentation.  These  cells  form  a  hollow  ball  of  cells  and  swim 
through  the  water  by  means  of  cilia.  Ultimately  this  little  animal 
settles  down  on  one  end  and  becomes  fixed  to  a  rock,  seaweed,  or 
pile.  The  free  end  becomes  indented  in  the  same  manner  as  a 
hollow  rubber  ball  may  be  pushed  in  on  one  side.  This  indented 
side  becomes  a  mouth,  tentacles  develop  around  the  orifice,  and 
we  have  an  animal  that  looks  very  much  like  the  hydra.  This 
animal,  now  known  as  a  hydroid  polyp,  buds  rapidly  and  soon 
forms  a  colony  of  little  polyps,  each  of  which  is  connected  with 
its  neighbor  by  a  hollow  food  tube.  The  hydroid  polyp  differs 
from  its  fresh- water  cousin,  the  hydra,  by 
usually  possessing  a  tough  covering  which 
is  not  alive. 

Hydroid  Colony  {Pennaria)}  —  (Material  put 
up  in  formol  may  be  handed  out  to  the  class  in 
small  vials).  In  the  portion  of  the  colony  you  have, 
where  are  the  polyps  located  ?  Examine  a  single 
polyp  and  make  out  all  you  can  regarding  (a)  its 
general  form,  (6)  the  position  of  tentacles,  (c)  the 
position  of  the  mouth.  The  buds  which  form  the 
free-swimming  medusae  are  frequently  found  bud- 
ding out  of  the  wall  of  the  polyp.  Can  you  de- 
scribe them? 

Demonstration.  —  Stained  polyps  and  part  of 
the  branch,  using  the  compound  microscope. 
Draw  part  of  a  colony  four  times  natural  size. 
Label  all  the  points  mentioned  above. 

Alternation  of  Generations  in  Coelen- 
terates.  —  The  lives  of  a  hydroid  and  a 
medusa  are  seen  thus  to  be  intimately  con- 
nected with  each  other.  A  hydroid  colony 
produces  new  polyps  by  budding.  This 
we  know  is  an  asexual  method  of  repro- 
duction. There  come  from  this  hydroid 
colony,  however,  little  buds  which  give  rise  to  medusae.     These 

1  See  Hvinter  and  Valentine,  MamuxL,  page  155. 


A  hydroid  colony  of  six  pobTJs; 
/,  feeding  polyp;  r,  repro- 
ductive polyp;  m,  a  medusa; 
y,  young  polyp. 


200 


ZOOLOGY 


medusse  produce  eggs  and  sperms.  Their  reproduction  is  sexual, 
as  was  the  reproduction  by  means  of  eggs  and  sperms  from  the 
prothallus  of  the  fern.  So  we  have  in  animals,  as  well  as  in 
plants,  an  alternation  of  generations. 

Sea  Anemone.  —  Those  who  have  visited  our  New  England  coast  are 
famihar  with  another  coelenterate  called  the  sea  anemone.  This  animal 
gets  its  name  from  the  fact  that,  seen  in  a  little  rocky  pool  along  the  shore, 
it  looks  like  a  beautiful  flower  of  a  golden  yellow  or  red  color.  The  body 
of  the  sea  anemone  is  like  the  hydra,  a  column  attached  at  one  end.     The 


Sea  anemone.  About  natural  size.  The  right-hand  specimen  is  expanded.  Note  the  mouth 
surrounded  by  the  tentacles.  The  left-hand  specimen  is  contracted.  From  model  at  the 
American  Museum  of  Natural  History. 

free  end  is  provided  with  a  mouth  surrounded  with  a  great  number  of 
tentacles.  These,  when  expanded,  look  like  the  petals  of  a  flower.  The 
sea  anemone  is  a  very  voracious  flower,  for  by  means  of  the  batteries  of 
stinging  cells  in  its  tentacles  it  is  able  to  catch  and  devour  fishes  and  other 
animals  almost  as  large  as  itself.  When  disturbed  or  irritated,  the  animal, 
like  the  hydra,  contracts  into  a  slimy  ball. 

Although  the  sea  anemone  is  like  a  large  hydra  in  appearance,  its  Interior 
is  different.  The  hollow  digestive  cavity  contains  a  number  of  partitions 
more  or  less  complete,  which  run  from  the  outer  wall  toward  the  middle 


CCELENTERATES 


201 


of  the  cavity.     Part  of  the  cavity,  as  in  the  hydra,  is  given  up  to  digesting 
the  food.     Food,  which  is  often  taken  ahve  into  the  body,  is  killed  by  means 
of  stinging  cells  found  in  the  long 
threadlike    tentacles     developed 
near  the  base  of  the  cavity. 

The  partitions  or  mesenteries, 
as  they  are  called,  are  usually 
double.  These  perform  in  the 
coral  polyp,  which  is  like  a  mini- 
ature sea  anemone  in  structure, 
a  very  important  function. 

Coral}  —  (Madreporic  coral  or 
our  common  Astrangia  may  be 
used  for  observations.)  Test  with 
a  drop  of  hydrochloric  acid. 
What  substance  is  present?  Ex- 
amine a  piece  of  the  ordinary 
white  branching  coral  (madre- 
pore) with  the  hand  lens.  Notice 
the  little  holes  at  intervals  over 

the  surface 
holes  ? 


A  branching  madreporic  coral. 

Do  you  find  little  partitions  in  these 


These  cuplike  depressions  were  once  occupied 
by  the  coral  animals  or  polyps,  each  in  its  own 
cup.  The  mesenteries  of  the  coral  polyp  are  double 
and  hollow  on  the  under  surface.  The  partitions 
seen  in  the  coral  cups  lie  between  these  mesenter- 
ies, and  are  formed  by  them  when  the  animal  is  alive. 
Sea  water  has  a  considerable  amount  of  lime  in  its 
composition.  This  lime  (calcium  carbonate)  is 
taken  from  the  water  by  certain  of  the  cells  of  the 
coral  polyp  and  deposited  around  the  base  of  the  ani- 
mal and  between  the  mesenteries,  thus  giving  the 
appearance  just  seen  in  the  cups  of  the  coral  branch. 
Asexual  Reproduction.  —  These  polyps  re- 
produce by  budding,  and  when  alive  cover  the 
whole  coral  branch  with  a  continuous  living  mass  of  polyps,  each  connected 
with  its  neighbor.  In  this  way  great  masses  of  coral  are  formed.  Coral, 
in  a  living  state,  is  alive  onlj?"  on  the  surface,  the  polyps  building  outward 
on  the  skeleton  formed  by  their  predecessors. 

Economic  Importance  of  Corals.  —  Only  one  (Astrangia)  of  a  great 
many  different  species  of  coral  lives  as  far  north  as  New  York.  In  tropical 
waters  they  are  very  abundant.  Coral  building  has  had  and  still  has  an  im- 
mense influence  on  the  formation  of  islands,  and  even  parts  of  continents  in 


A  single  coral  cup,  showing 
the  walls  of  lime  built  by 
the  mesenteries.  From 
a  photograph  loaned  by 
the  American  Museum 
of  Natural  History. 


1  See  Hunter  and  Valentine,  Manual,  page  157. 


202  ZOOLOGY 

tropical  seas.  Not  only  are  many  of  the  West  Indian  islands  composed 
largely  of  coral,  but  also  Florida,  Australia,  and  the  islands  of  the  southern 
Pacific  are  almost  entirely  of  coral  formation. 

Coral  Reefs.  —  The  coral  polyp  can  live  only  in  clear  sea  water 
of  moderate  depth.  Fresh  Avater,  bearing  mud  or  other  impurities,  kills 
them  immediately.  Hence  coral  reefs  are  never  found  near  the  mouths 
of  large  fresh-water  rivers.  They  are  frequently  found  building  reefs  close 
to  the  shore.  In  such  cases  these  reefs  are  called  fringing  reefs.  The  so- 
called  barrier  reefs  are  found  at  greater  distance  (sometimes  forty  to  fifty 
miles)  from  the  shore.  An  example  is  the  Great  Barrier  Reef  of  Australia. 
The  typical  coral  island  is  called  an  atoll.  It  has  a  circular  form  inclosing 
a  part  of  the  sea  which  may  or  may  not  be  in  communication  with  the 
ocean  outside  the  atoll.  The  atoll  was  perhaps  at  one  time  a  reef  outside 
a  small  island.  This  island  disappeared,  probably  by  the  sinking  of  the 
land.  The  polyps,  which  could  live  in  water  up  to  about  one  hundred  and 
fifty  feet,  continued  to  build  the  reef  until  it  arose  to  the  surface  of  the 
ocean.  As  the  polyps  could  not  exist  for  long  above  low  water  line,  the 
animals  died  and  their  skeletons  became  disintegrated  by  the  action  of  waves 
and  air.  Later  birds  brought  a  few  seeds  there,  perhaps  a  cocoanut  was 
washed  ashore ;  thus  plant  life  became  established  in  the  atoll  and  a  new 
outpost  to  support  human  life  was  thus  established. 

Classification  of  Ccelenterates 

Class  I.     Hydrozoa.     Body  cavity  containing  no  mesenteries,  usually  alternation 

of  generation.     Examples  :  Hydra,  hydroid  pennaria. 
Class  II.     Scyphozoa.     Examples  :   large  jellyfishes. 
Class  III.     Actinozoa.     Mesenteries    present    in    body    cavity.      Examples ;    sea 

anemones  and  corals. 
Class  IV.     Ctenophora. 

Reference  Books 
for  the  pupil 

Herrick,  Text-book  in  General  Zoology,  Chap.  VII.     American  Book  Company. 
Davison,  Practical  Zoology,  pages   167-175.     American  Book  Company. 
Holder,  Half  Hours  with  the  Lower  Animals.     American  Book  Company. 

FOR    THE    TEACHER 

Agassiz,  A  First  Lesson  in  Natural  History.     D.  C.  Heath  and  Company. 
Dana,  Coral  and  Coral  Islands.     Dodd,  Mead,  and  Company. 
Parker,  Elementary  Biology.     The  Macmillan  Company. 


XVI.     THE   STARFISH   AND   ITS   ALLIES 


Stricture  of  a  Star  fish. \— A  g^nce  at  the  body  of  a  starfish  shows  us 
that  the  name  is  rightly  given.  The  body  is  called  the  disk;  the  five  racU- 
ating  structures  the  arms  or  rays.  The  term  echinoderm  (leaning  spinv- 
us^ll  sir^^^Thesl^elt^^^  ^^  examination  of  the  dried  specim/n  b^fo?e 
the  animal  is  literally  em- 
bedded in  the  skin  and  pro- 
trudes as  many  thousands  of 
little  spines.  Closer  examina- 
tion reveals  the  fact  that  the 
skeleton  is  composed  of  very 
many  tiny  plates,  all  articu- 
lated together  in  such  a  way 
as  to  give  great  flexibility  as 
well  as  strength  to  the  frame- 
work of  the  starfish. 

Notice  that  the  thin  skin 
covers  the  skeleton,  but  that 
in  a  ray  broken  in  cross  sec- 
tion the  interior  of  the  ray  is 
hollow.  In  the  starfish  the 
arms  have  the  position  of  radii 
of  a  circle;  hence  the  animal 
is  said  to  be  radially  symmet- 
rical. 

Notice  the  differences  be- 
tween the  dorsal  and  ventral 
surfaces.  The  latter  is  called 
the  oral  surface  because  of  the 
position  of  the  mouth,  which 
can  be  seen  as  a  hole  in  the 
center  of  the  disk.  In  living 
specimens  the  baglike  stomach 
is  frequently  found  projecting 
from  this  hole. 

The  five  grooves,  which  lead  outward  along  the  rays  from  the  area  around 
the  mouth,  are  known  as  the  amhulacral  grooves  because  they  contain  the 
ambulacroB  or  tube  feet.  In  the  dried  specimen  the  tube  feet  may  be  found 
as  very  small  dried  projections  in  the  grooves.  There  are  four  rows  of 
tube  feet  in  each  groove.  Estimate  the  number  of  tube  feet  in  a  single  row 
and  thus  figure  out  the  number  of  tube  feet  in  a  starfish.  Do  you  believe 
the  number  to  be  exactly  the  same  for  every  starfish?  Give  reasons  for 
your  answer.  Locomotion  in  the  starfish  is  performed  by  the  movement 
of  hundreds  of  the  little  suckerlike  feet.  The  process  of  movement  of  a 
single  tube  foot  is  a  complicated  one.  It  is  performed  partly  by  means 
of  muscles,  but  chiefly  by  means  of  the  passage  of  water  through  a  system 
of  water  tubes  within  the  body  of  the  animal. 

*  See  Hunter  and  Valentine,  Manvxd,  page  147. 

203 


Ventral  or  under  surface  of  the  starfish.  The  dark 
circle  in  the  middle  is  the  mouth,  from  which 
radiate  the  five  ambulacral  grooves,  each  filled 
with  four  rows  of  tube  feet.  Photograph  half 
natural  size,  by  Davison. 


204 


ZOOLOGY 


'St  ■■..    a  I 


^ 


%1^^M 


Vertical  section  through  one  arm  of  a  starfish;  b,  ampulla;  d,  water  canal  opening  at  maJre- 
poric  plate  {st);  i,  radial  water  tube;  m,  mouth;  ft,  tube  feet;  py,  digestive  gland;  stc, 
stomach.    Davison,  Zoology. 

On  the  dorsal  (aboral)  side  of  the  animal  you  will  find  a  raised  body  about 
the  diameter  of  a  pencil.  This  body,  which  under  the  microscope  has  the 
structure  of  a  very  fine  sieve,  is  called  the  madreporic  plate.  Through  this 
plate  water  passes  into  a  system  of  water  tubes  and  reservoirs.  These  tubes 
extend  ultimately  into  the  rays,  there  ending  in  the  individual  tube  feet. 

Method  of  Locomotion.  —  If  we  could  examine  the  connection  of  a 
tube  foot  with  the  system  of  water  canals,  we  should  find  that  water  pass- 
ing from  the  canals  in  the  rays  flows  into  a  tiny  receptacle  connected  with 
the  tube  foot.  If  the  tube  foot  is  to  be  extended,  the  muscles  in  the  wall 
of  the  ampulla  (the  receptacle  next  the  tube  foot)  contract.  This  forces  the 
water  out,  closing  a  tiny  valve  on  the  side  of  the  radial  canal  and  sending 
the  water  into  the  tube  foot,  thus  causing  it  to  lengthen.  The  end  of  the 
tube  foot  is  composed  of  a  little  disk  of  muscle,  thicker  at  the  outer  side 
than  on  the  inner.  When  this  disk  is  placed  against  an  object,  and  when 
water  is  withdrawn  from  the  tube  foot  into  the  ampulla,  the  disk  becomes 
fastened  again  by  suction.  If  now  the  muscles  in  the  wall  of  the  tube 
foot  contract,  and  this  process  takes  place  simultaneously  and  in  hundreds 

of  the  feet,  it  can  be  seen  that  the  body  of  the 
starfish  is  drawn  forward  a  short  distance.  To 
release  the  tube  foot  water  is  pumped  in  from 
the  ampulla  by  the  process  mentioned  above. 
The  same  act  repeated  again  and  again  results 
in  locomotion  at  the  rate  of  about  six  inches  per 
minute  in  an  adult  starfish. 

The  Nervous  System  and  its  Work.  —  The 
movements  of  the  tube  feet,  although  not  in 
unison,  are  coordinated  to  act  for  a  common 
purpose.  If  the  animal  starts  to  move  in  a  given 
direction,  the  tube  feet  in  the  different  rays  all 
pull  in  the  same  direction.  It  has  been  found 
that  this  is  due  to  the  presence  of  a  ring  of 
nervous  tissue,  strands  of  which  extend  out  into 


Diagram  of  nervcus  system  of 
s  t  a  r  fi  s  h  ;  r,  nervous  ring 
around  mouth;  n,  radial 
nerves  to  each  arm,  ending 
at  the  eye. 


THE  STARFISH  AND   ITS   ALLIES  205 

each  ray,  ending  on  the  muscles  of  the  tube  feet.  If  this  nerve  ring  is  cut, 
then  the  different  rays  do  not  act  together,  but  one  set  of  tube  feet  pull  in 
one  direction  and  those  of  another  ray  pull  in  another,  thus  preventing 
locomotion.  At  the  extreme  end  of  each  ray  the  nerve  is  found  to  end  in 
a  tiny  eye  spot.  In  your  specimen  it  may  show  as  a  salmon-pink  spot  at 
the  outer  end  of  the  ambulacral  groove.  This  eye  spot  probably  cannot 
distinguish  form,  but  by  means  of  it  the  starfish  can  distinguish  between 
light  and  darkness. 

Organs  of  Breathing.  —  The  starfish  spends  most  of  its  life  in  the  water, 
although  it  may  be  found  attached  to  rocks  or  under  moist  seaweed  after 
the  tide  has  receded.  In  common  with  all  animals  and  plants  it  must  have 
oxygen.  Some  oxygen  is  taken  in  with  the  water  in  the  system  of  water 
tubes  within  the  body,  and  some  is  taken  out  of  the  water  by  means  of  delicate 
fingerlike  processes  of  the  skin  called  branchice.  The  branchiae  protrude  from 
between  the  spines  of  the  dorsal  surface.  They  may  be  withdrawn  by  the 
animal.  They  are  much  too  delicate  to  withstand  drying  and  cannot  be 
seen  on  the  specimen  you  are  studying. 

Food  of  the  Starfish.  —  The  food  and  method  of  feeding  are  of  con- 
siderable interest  to  us  because  of  the  economic  value  of  the  clams, 
oysters,  and  other  mollusks  on  which  the  starfish  feed.  Starfish  are  enor- 
mously destructive  of  young  clams  and  oysters,  as  the  following  evidence, 
collected  by  Professor  A.  D.  Mead  of  Brown  University,  shows.  A  single 
starfish  was  confined  in  an  aquarium  with  fifty-six  young  clams.  The 
largest  clam  was  about  the  length  of  one  arm  of  the  starfish,  the  smallest 
about  ten  millimeters  in  length.  In  six  days  every  clam  in  the  aquarium 
was  devoured.  The  method  of  capturing  and  killing  their  prey  shows  that 
they,  in  some  instances,  appear  to  smother  the  mollusk  by  wrapping  around 
it  with  their  soft  baggy  stomach.  The  latest  evidence  on  the  subject,  how- 
ever, seems  to  show  that  they  wrap  around  the  valves  of  the  mollusk  and 
actually  pull  apart  the  valves  by  means  of  their  tube  feet,  some  of  which 
are  attached  to  one  valve  and  some  to  the  other  of  their  victim.  Once  the 
soft  part  of  the  mollusk  is  exposed,  the  stomach  envelops  it  and  it  is  rapidly 
digested  and  changed  to  a  fluid. ^  This  it  can  do  because  of  the  five  large 
digestive  glands  which  occupy  a  large  part  of  each  ray,  and  which  pour 
their  digestive  fluids  into  five  pouchlike  extensions  of  the  stomach  extend- 
ing into  each  ray. 

Damage  to  the  amount  of  thousands  of  dollars  is  done  annually  to  the 
oysters  in  Connecticut  alone,  by  the  ravages  of  starfish.  During  the  sum- 
mer months  the  oyster  boats  are  to  be  found  at  work  raking  the  beds  for 
starfish,  which  are  collected  and  thrown  ashore  by  the  thousands. 

'  Observation  by  one  of  my  pupils,  F.  T.  Lacy,  seems  to  show  that  in  the  case 
of  the  mussel  the  starfish  inserts  part  of  the  stomach  into  the  hole  through  which 
the  byssus  protrudes,  and  kills  the  mussel  by  means  of  the  digestive  fluid.  When 
the  shells  gape,  the  starfish  finishes  the  meal  at  its  leisure. 


206 


ZOOLOGY 


Starfish,  showing  regeneration  of  lost 
arms.  Notice  that  in  the  lowest 
specimen  the  arm  is  just  begin- 
ning to  regenerate. 


Regeneration.  —  It  is  no  uncommon 
thing  to  find  starfish  with  fewer  arms  than 
the  normal  number.  In  such  specimens 
small  arms  are  frequently  seen,  making  it 
appear  likely  that,  once  having  lost  an  arm, 
it  might  grow  again.  Such  is  indeed  the 
case,  the  starfish  having  the  ability  to  re- 
generate (grow  anew)  lost  parts.  If  a  star- 
fish should  lose  all  five  rays,  it  is  possible 
that  under  favorable  conditions  it  might 
regenerate  all  its  lost  parts  and  become  as 
active  as  ever  in  the  destruction  of  shellfish. 

Development.  —  Besides  this  asexual 
method  of  regeneration,  the  starfish  repro- 
duces sexually  by  means  of  eggs  and  sperms. 
The  sexes  are  separate.  The  eggs  are  passed 
into  the  water;  fertilization  takes  place 
near  the  surface  of  the  water,  where  the  eggs 
and  sperms  are  found  in  great  numbers 


during  the  breeding  season  (June-July  in  Long  Island  Sound).  Develop- 
ment proceeds  at  first  as  in  the  jellyfish,  the  egg  segmenting  to  form 
a  blastula  and  gastrula.  Development  does  not  proceed  directly  into  a 
starfish,  however,  the  animal  being  at  first  very  unlike  the  adult.  It  swims 
freely  until  a  limy  skeleton  is  developed.  The  starfish  larva  eventually 
buds  off  a  tiny  star-shaped  body  which  actually  lives  on  the  tissues  of  the 
larva,  eventually  becoming  a  tiny  starfish  no  larger  than  a  small  pin  head. 
At  this  stage  of  their  existence  they  are  foiuid  on  eelgrass  and  other  salt- 


Sea  urchins  (Arbacia)  showing  mouth,  tube  feet,  and  movable  spines. 


THE  STARFISH  AND  ITS   ALLIES  207 

water  plants.  A  rapid  increase  in  size  takes  place  at  this  time ;  the  young 
after  two  weeks  at  the  most  go  to  the  bottom  and  begin  their  life  there. 
It  is  estimated  that  if  seaweed  should  be  taken  out  of  the  water  during  the 
months  of  June  and  July  in  the  region  of  Long  Island  Sound,  enough 
young  starfish  would  be  killed  to  save  over  six  million  clams  per  week  for 
each  wagon-load  of  seaweed  removed. 

Other  Echinoderms.  —  Other  echinoderms,  which  are  frequently  seen, 
but  which  have  less  economic  importance,  are  the  sea  urchins,  sand  dollars, 
sea  cucumbers,  and  sea  lilies  or  crinoids. 

The  sea  urchin  is  found  all  along  our  northern  coast,  living  in  the  tide 
pools  along  the  shore  and  also  in  deep  water  off  the  coast. 

The  body  of  the  sea  urchin  is  almost  hemispherical  in  general  form,  and 
is  provided  with  a  large  number  of  long  spines,  which  are  movable.  Loco- 
motion is  performed  by  means  of  the  tube  feet,  as  in  the  starfish,  but  the 
spines  are  used  to  some  extent  as  levers.  Food  is  ground  up  by  means  of 
a  set  of  five  strong  teeth,  placed  just  within  the  mouth. 

The  sand  dollar  is  a  very  much  flattened  form  of  starfish,  modified  to 
withstand  the  pressure  of  the  deep  water  in  which  it  is  found.  Another 
deep-sea  form  is  the  basket  star,  a  much-branched,  five-armed  form.  Others 
are  the  brittle  stars,  so  called  from  their  habit  of  casting  off  their  arms  when 
disturbed. 

The  sea  cucumber  has  a  leathery  skin,  only  fragments  of  lime  being  found 
scattered  through  it.  The  internal  structure  is  much  like  that  of  the  starfish. 
It  has  the  curious  habit  of  ejecting  all  its  digestive  organs  when  disturbed. 

The  crinoids  were  once  far  more  common  than  they  are  to-day.  Their 
fossil  remains  form  a  large  part  of  some  of  our  limestone  rocks. 

Classification  of  Echinoderms 

Class  I.     Crinoidea.    Mostly  extinct  forms.     Deep-sea  attached  forms.    Example, 

crinoid  (sea  lily). 
Class  II.    Asteroidea.     Free  mo\dng,  usually  five-armed  echinoderms.     Example, 

starfish. 
Class  III.    Ophiuroidea.     Free  moving  echinoderms  with  movable  arms  distinct 

from  disk.     Example,  brittle  star. 
Class  IV.     Echlnoidea.     Echinoderms  with  no  free  arms,    spines  usually  movable 

and  well  developed.     Examples,  sea  urchin  and  sand  dollar. 
Class  V.     Holothurioidea.     Soft  bodied  forms,  the  skeleton  consisting  of  scattered 

limy  spicules.    Example,  sea  cucvunber. 

Reference  Books 
for  the  teacher 

Dodge,  General  Zoology,  pages  87-95.     American  Book  Company. 
Parker  and  Haswell.    A  Text-book  of  Zoology.    The  Macmillan  Company. 


XVII.     WORMS 

The  Earthworm.  —  The  earthworm  belongs  to  a  group  of  animals 
called  the  annelids.  They  are  so  called  because  the  body  is  made 
up  of  a  large  number  of  rings  or  segments.    (Lat.  annulus,  a  ring.) 

Study  a  living  worm  in  order  to  answer  the  following  questions. 

Careful  study  of  several  worms  will  show  that  the  number  of  segments 
varies,  the  larger  worms  having  more  segments.  Do  the  segments  vary 
greatly  in  width?     In  shape? 

Notice  the  color  of  the  worm;  is  it  like  that  of  the  ground  in  which  it 
hves?     Do  the  dorsal  and  ventral  surfaces  differ  in  color?     Can  you  ac- 


The  earthworm.     Note  the  swollen  area,  the  clitellum.     Photographed  Viy  Overton. 

count  for  this?  The  earthworm  is  an  example  of  a  bilaterally  symmetrical 
animal,  that  is,  one  in  which  the  right  side  is  a  counterpart  of  the  left  side. 
Compare  with  the  starfish  or  sea  anemone.  Are  the  latter  animals  also 
bilaterally  as  well  as  radially  symmetrical  ? 

The  two  ends  of  the  worm  differ  somewhat  in  appearance,  the  anterior 
end  being  pointed  and  the  posterior  rather  flattened.  Tests  made  with  a 
pencil  or  other  pointed  object  will  show  which  end  is  more  sensitive  to  touch. 
Which  end  usually  goes  first  in  crawling? 

Measure  an  earthworm  when  it  is  extended  and  compare  with  the  same 
worm  contracted.  Note  the  difference  in  length.  This  is  accounted  for 
when  we  understand  the  method  of  locomotion.  Under  the  skin  are  two 
sets  of  muscles,  an  outer  set  which  passes  in  a  circular  direction  around  the 
body,  and  an  inner  set  which  runs  the  length  of  the  body.  The  body  is 
lengthened  by  the  contraction  of  the  circular  muscles.  How  might  the 
body  of  an  earthworm  be  shortened  ? 

Put  your  finger  over  the  under  surface  of  the  worm.  Notice  the  rough- 
ness.    Examine  the  surface  with  a  hand  lens.     Four  rows  of  very  minute 

^  See  Hunter  and  Valentine,  Manual,  page  131. 

208 


WORMS 


209 


bristles  called  sdce  may  be  found.     Determine  if  these  rows  are  single  or 
double.     How  many  setse  to  a  segment? 

Every  segment  except  the  first  three  and  the  last  is  provided  with  set«. 
Each  seta  has  attached  to  it  small  muscles,  which  turn  the  seta  so  it  may 
point  in  the  opposite  direction  from  which  the  worm 
is  moving.  If  you  watch  your  specimen  carefully,  you 
will  see  that  locomotion  is  accomplished  by  the  thrusting 
forward  of  the  anterior  end ;  then  a  wave  of  muscular 
contraction  passes  dov\'n  the  body,  thus  shortening  the 
body  by  drawing  up  the  posterior  end.  The  seta?  at  the 
anterior  end  serve  as  anchors  which  prevent  the  body 
from  slipping  backward  as  the  posterior  end  is  drawn  up. 

Make  a  drawing  of  several  segments  to  show  the  ar- 
rangement of  setse. 

Notice  that  living  earthworms  tend  to  collect  along 
the  sides  of  a  dish  or  in  the  corners.  This  seems  to 
be  due  to  an  instinct  which  leads  them  to  inhabit  holes 
in  the  ground. 

Test  a  worm  by  placing  half  in  and  half  out  of  a  darkened  box.  Which 
does  it  seem  to  prefer,  light  or  darkness?  There  are  no  eyes  visible.  A 
careful  study  of  the  worm  with  the  microscope,  however,  has  revealed  the 
fact  that  scattered  through  the  skin  of  the  anterior  segments  are  many  little 
structures  which  not  only  distinguish  between  light  and  darkness,  but  also 
light  of  low  and  high  intensity,  as  well  as  the  direction  from  which  it  comes. 
A  worm  has  no  ears  or  special  organs  of  feeling.  We  know  that  although 
a  worm  responds  only  to  vibration's  of  low  pitch,  the  sense  of  touch  is  well 
developed  in  all  parts  of  the  bod,y.  Notice  especially  how  the  worm  uses 
the  whole  anterior  end  to  feel  with.  Jar  the  dish  in  which  the  worm  rests 
hghtly,  and  note  the  reaction  that  takes  place. 

Feeding  Habits.  —  Worms  may  be  kept  in  the  laboratory  for 
some  time  in  a  glass  dish  or  box  filled  with  soil.  They  feed  on 
pieces  of  lettuce  or  cabbage  leaf.     A  feeding  worm  will  show  the 


Diagram  to  show  how 
movement  of  a  seta 
is  accomplished; 
M,  muscles;  ,S',  seta; 
W,  body  wall. 
(After  Sedgwick  and 
Wilson.) 


Forepart  of  an  earthworm  with  the  left  body  wall  removed;  a,  dorsal  blood  vcssri;  b,  brain; 
c,  crop;  g,  gizzard;  i,  intestine;  k,  nephridia;  m,  mouth;  n,  one  of  the  ganglia  of  the  nerve 
cord;  oe,  esophagus;  p,  pharynx;  v,  ventral  blood  vessel.    Davison,  Zoology. 

proboscis,  an  extension  of  the  upper  lip  which  is  used  to  push 
food  into  the  mouth.  The  earthworm  is  not  provided  with  hard 
jaws  or  teeth.     Yet  it  literally  eats  its  way  through  the  hardest 

hunter's   BIOL. — 14 


210 


ZOOLOGY 


Diagrammatic  cross  section  of  the  body  of  a 
coelenterate  A,  and  that  of  a  worm  B, 


soil.  Inside  the  mouth  opening  is  a  part  of  the  food  tube  called 
the  pharynx.  This  is  very  muscular  so  that  it  can  be  extended  and 
withdrawn  by  the  worm.  When  applied  to  the  surface  of  any  small 
pebble  or  leaf,  it  acts  as  a  suction  pump  and  draws  it  into  the 
food  tube.  As  the  worms  take  organic  matter  out  of  the  ground 
as  food,  they  pass  the  earth  through  the  body  in  order  to  get  this 

food.  The  earth  is  mixed 
with  fluids  poured  out  from 
glands  in  the  food  tube,  and 
is  passed  out  of  the  body 
and  deposited  on  the  sur- 
face of  the  ground,  in  the 
form  of  little  piles  of  moist 
earth.  These  are  familiar 
sights  on  all  lawns;  they 
are  called  worm  casts. 
Charles  Darwin  calculated  that  fifty ythree  thousand  worms  may  be 
found  in  an  acre  of  ground,  and  that  ten  tons  of  soil  might  pass 
through  their  bodies  in  a  single  year  to  be  brought  to  the  surface. 
Earthworms,  in  spite  of  their  fondness  for  some  garden  vegetables 
and  young  roots,  do  an  immense  amount  of  good  by  breaking  up 
the  soil,  thus  allowing  water  and  oxygen  to  penetrate  to  the  roots 
of  plants. 

Comparison  between  Hydra  and  Worm.  —  The  digestive  tract  of 
the  worm  is  an  almost  straight  tube  inside  of  another  tube.  The 
latter  is  divided  by  partitions  which  mark  the  boundary  of  each 
segment.  The  outer  cavity  is  known  as  the  body  cavity.  In  the 
hydra  no  distinction  existed  between  the  body  cavity  and  digestive 
tract.  In  the  animals  higher  than  the  ccelenterates  the  digestive 
tract  and  body  cavity  are  distinct.  The  digested  food  material 
passes  by  osmosis  into  the  body  cavity.  Some  food  reaches  the 
blood  vessels  and  is  pumped  over  the  body,  most  of  it  is  used  by 
the  organs  which  it  bathes.  Nitrogenous  waste  is  excreted  from 
each  segment  through  a  pair  of  coiled  tubules  called  nephridia. 

Course  of  Blood.  —  In  a  large  earthworm  the  course  of  the 
blood  is  easy  to  follow.  Notice  the  position  of  the  dorsal  blood 
vessel.     Watch  it  at  one  point.    The  blood  vessel  expands  as  the 


WORMS 


211 


blood  passes  slowly  forward.  The  whole  dorsal  blood  vessel,  and 
especially  several  tubes  which  connect  it  with  a  ventral  vessel  on 
the  opposite  side,  are  contractile.  These  connecting  tubes  are 
known  as  hearts,  because  they  serve  to  pump  the  blood  in  a 
definite  direction.  Compare  the  rate  of  pulsation  with  your  own 
pulse. 

Respiration.  —  No  gills  or  lungs  are  present,  the  thin  skin  acting 
as  an  organ  of  respiration.  But  the  worm  is  unable  to  take  in 
oxygen  unless  the  membranelike  skin  is  kept  moist.  Respiration 
in  the  earthworm  is  simply  the  exchange  or  osmosis  of  gases 
through  the  skin,  the  oxygen  passing  into  the  blood,  the  carbon 
dioxide  formed  from  the  oxidation  taking  place  within 
the  body  of  the  worm  passing  out. 

Development.  —  Notice  in  some  worms  the  swollen  area 
(about  one  third  the  distance  from  the  anterior  end)  called  the 
girdle  or  clitellum.  This  area  forms  a  little  sac  in  which  the 
eggs  of  the  worm  are  laid.  As  it  passes  toward  the  anterior 
end  of  the  worm,  it  receives  the  sperms  and  a  nutritive  fluid 
in  which  the  eggs  live.  The  fertilized  eggs  are  then  left  to 
hatch.  The  capsules  may  be  found  in  manure  heaps,  or  under 
stones  in  May  or  June ;  they  are  small  yellowish  or  brown  bags 
about  the  diameter  of  a  worm.  If  possible,  procure  some 
young  worms  and  compare  them  with  older  ones. 

Regeneration.  —  Earthworms  possess  to  a  large  degree 
the  power  of  replacing  parts  lost  through  accident  or  other 
means.  The  anterior  end  may  form  a  new  posterior  end, 
while  the  posterior  end  must  be  cut  anterior  to  the  clitellum 
to  form  a  new  anterior  end.  This  seems  to  be  in  part  due  to 
the  greater  complexity  of  the  organs  in  the  anterior  end. 

The  Sandworm.  —  Other  segmented  worms  are  familiar 
to  some  of  us.  The  sandworm,  used  for  bait  along  our 
eastern  coast,  is  a  segmented  worm  which  lives  between  tide 
marks  in  sandy  localities.  It  is  plainly  segmented,  each  seg- 
ment bearing  a  pair  of  locomotor  organs  called  parapodia 
(meaning  side  feet).  A  part  of  each  parapodium  is  prolonged 
into  a  triangular  gill.  The  animal  has  a  distinct  head,  which 
is  pro^dded  with  tentacles,  palps,  and  eye  spots.  The  mouth  has  a  pair  r! 
hard  jaws  which  may  be  protruded.  In  this  way  the  animal  seizes  and 
draws  prey  into  its  mouth.  The  sandworm  swims  near  the  surface  of  the 
water,  the  body  bending  in  graceful  undulations  as  the  parapodia.  like  little 
oars,  force  the  worm  forward.      They  spend  most  of  the  time  in  tubes  in 


A  marine  worir 
{Nerds). 


212 


ZOOLOGY 


the  sand;  these  tubes  are  constructed  of  slime  excreted  from  the  body  of 
the  worm.^ 

The  Leech.  —  The  common  leech  or  bloodsucker  is  a  flattened  seg- 
mented worm,  inhabiting  fresh-water  ponds  and  rivers.  The  adult  i? 
provided  with  two  sucking  disks,  by  means  of  which  it  fastens  itself  to 
objects.  The  mouth  is  on  the  lower  surface  close  to  the  anterior  disk. 
Locomotion  is  accomplished  by  swimming  or  by  means  of  the  suckers, 
somewhat  after  the  manner  of  a  measuring  worm.  They  feed  greedily 
and  are  often  found  gorged  with  blood,  which  they  suck  from  the  body 
of  the  victim.  Discomfort,  but  no  danger,  attends  the  bite  of  the  blood- 
sucker, so  dreaded  by  the  small  boy. 

Unsegmented  Worms.  —  Some  worms  are  unsegmented ;  such 
are  the  flatworms  and  roundworms.     A  common  leaflike  form  of 

flat  worm  may  be  found 
clinging  to  stones  in 
our  fresh  water  ponds 
or  brooks.  Most  flat- 
worms  are,  however, 
parasites  on  other  ani- 
mals. Of  much  in- 
terest to  us  is  the  life 
history  of  the  flatworm 
infesting  the  liver  of 
sheep,  causing  the  dis- 
ease called  liver  rot, 
which  causes  annually  a  loss  of  several  millions  of  dollars' 
worth  of  sheep.  This  worm  is  called  the  liver  fluke  because 
of  its  abode  in  the  liver  of  the  sheep.  The  developing  eggs 
pass  out  from  the  liver  into  the  intestine  and  thence  outside 
of  the  body.  If  the  egg  happens  to  be  deposited  in  water, 
it  develops,  otherwise  it  dies.  The  embryo  is  a  little  oval,  ciliated 
creature,  microscopic  in  size.  This  embryo  swims  about  until  it 
reaches  a  water  snail.  Here  it  lives  as  a  parasite,  loses  its  cilia, 
becomes  larger,  and  gives  rise  to  a  number  of  little  larvae  called 
redice.  The  redise  give  rise  to  more  larvae,  some  like  themselves 
and  others  tadpole-shaped.     The  latter  larvae  leave  the  snail,  swim 


A  flatworm  (Yungia  Aurantiaca),  much  magnified.    From 
model  in  the  American  Museum  of  Natural  History. 


*  If  the  li\'ing  sandworm  is  obtainable,  a  laboratory  period  may  be  devoted  to 
its  activities.     See  Hunter  and  Valentine,  Manual^  page  133. 


WORMS 


213 


to  the  shore  of  the  pond,  and  encyst  themselves  in  the  grass  near 

its  border.      If  this  grass  is  eaten  by  sheep,  the  encysted  larvje 

(called  cercarice)  are  taken 

into  the  digestive  tract  and 

then    develop    into     adult 

hukes. 

Cestodes  or  Tapeworms. — 
These  parasites  infest  man 
and  many  other  vertebrate 
animals.  The  tapeworm 
(Tcenia  solium)  passes 
through  two  stages  in  its 
life  history,  the  first  within 
a  pig,  the  second  within  the 
intestine  of  man.  The  eggs 
of  the  worm  are  taken  in 
with  the  pig's  food.  The 
worm  develops  within  the 
intestine  of  the  pig,  but 
soon  makes  its  way  into  the 
muscles.  If  man  eats  pork 
containing  these  worms,  he 

may  become  a  host  for  the  tapeworm.  The  animal,  which  at  this 
stage  consists  of  a  round  headlike  part  provided  with  hooks,  fastens 
itself  to  the  wall  of  the  intestine.  This  head  now  buds  off  a  series 
of  segmentlike  structures,  which  are  practically  bags  full  of  eggs. 
These  structures,  called  proglottids,  break  off  from  time  to  time, 
thus  allowing  the  eggs  to  escape.  The  proglottids  have  no  separate 
digestive  systems,  but  the  whole  body  surface,  bathed  in  digested 
food,  absorbs  it  and  is  thus  enabled  to  grow  rapidly. 

Roundworms.  —  Still  other  wormlike  creatures  called  round- 
worms are  of  importance  to  man.  Some,  as  the  vinegar  eel  found 
in  vinegar,  or  the  pinworms  parasitic  in  the  lower  intestine  of 
man,  do  little  or  no  harm.  The  pork  worm  or  Trichina,  however, 
is  a  parasite  which  may  cause  serious  injury.  It  passes  through 
the  first  part  of  its  existence  as  a  parasite  in  a  pig  or  other  verte- 
brate (dog,  cat,  ox,  or  horse),  where  it  encysts  itself  in  the  muscles 


Development  of  the  liver  fluke;  A,  ciliated  larva; 
B,  sporocyst,  containing  new  sporocyst  (r),  and 
redia(m.);  C,  redia,  containing  daughter  rediaand 
tadpolelike  cercaria;  D,  fully  developed  cercaria. 


214  ZOOLOGY 

of  its  host.  In  the  case  of  pork,  if  the  meat  is  eaten  in  an  un- 
cooked condition,  the  cyst  is  dissolved  off  by  the  action  of  the 
digestive  fluids,  and  the  living  trichina  becomes  free  in  the  intestine 
of  man.  Here  it  bores  its  way  through  the  intestine  walls  and 
enters  the  muscles,  causing  inflammation  there.  This  causes  a 
painful  disease  known  as  trichinosis. 

Some  roundworm  parasites  live  in  the  skin,  and  others  live  in 
the  intestines  of  the  horse.  Still  others  are  parasitic  in  fish  and 
insects,  one  of  the  commonest  being  the  hair  snake,  often  seen  in 
country  brooks. 

Classification  of  Segmented  Worms  (Anntjlata) 

Class  I.     Chcetopoda  (bristle-footed).     Segmented  worms  having  setse. 

Subclass  I.     Polychceta  (many  bristles).     Having  parapodia  and  usually  head 

and  gills.     Example,  sandworm. 
Subclass  II.     Oligochceta    (few   bristles).      No    parapodia,  head,  or  gills.     Ex- 
ample, earthworm. 
Class  II.     Discophora  (bearing  suckers).     No  bristles,  two  sucking  disks  present. 
Example,  leech. 

Platyhelminthes  (Flatworms) 

Body  flattened  in  dorso- ventral  direction. 

Class  I.  Turbellaria.  Small  aquatic,  mostly  not  parasitic.  Example,  planarian 
worm. 

Class  II.  Trematoda.  Usually  parasitic  worms  which  have  complicated  life 
history.     Example,  liver  fluke  of  sheep. 

Class  HI.  Cestoda.  Internal  parasites  ha^'ing  two  hosts.  Example,  tape- 
worm. 

Nemathelminthes  (Roundworms) 

Threadlike    worms,    mostly    parasitic.      Examples,   vinegar    eel    and 
Trichina. 

Reference  Books 

for  the  pupil 

Davison,  Practical  Zoology,  pages  150-161.     American  Book  Company. 
Herrick,  Text-book  in  General  Zoology,  Chap.  TX.     American  Book  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies,  VI.     D.  Appleton  and  Company. 

FOR   THE    teacher 

Darwin,  Earthworms  and  Vegetable  Mould.     D.  Appleton  and  Company. 
Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 


XVIII.    CRUSTACEANS 

The  Crayfish  (Cambarus  affinis).  —Crayfish  live  in  fresh- water 
lakes  and  streams.  There  they  may  be  caught  under  projecting 
stones  in  clear  streams  by  hand.  From  muddy  streams  they  may 
be  taken  by  means  of  a  weighted  net,  which  is  pulled  along  the 
bottom.  Although  they  prefer  the  water,  they  are  sometimes 
found  at  some  distance  from  any  large  body  of  water;  such 
animals  are  supposed  to  be  migrating. 


Crayfish;  A.,  antennie;  E.,  stalked  eye;  C.P.,  cephalothorax;  .46.,  abdomen;  C.F.,  caudal 
fin;  M.,  mouth;    Ch.,  chelipeds.    From  photograph. 

The  Structure  and  Activities  of  the  Crayfish.  —  Living  crayfish  in  dishes 
of  water  should  be  provided  for  this  exercise  *  Notice  the  color  of  the 
living  crayfish.  In  the  natural  habitat  the  colors  blend  with  its  surround- 
ings, so  that  it  is  difficult  to  distinguish  a  crayfish  from  the  bottom  on  which 
it  rests.     The  animal  is  thus  said  to  be  protectively  colored. 

The  body  is  composed  of  a  series  of  rings  or  segments.  Tliis  fact  is  not 
apparent  at  the  anterior  end  of  the  body,  where  the  head  and  mifldle  region 
(thoracic  region)  are  covered  by  one  piece  of  the  skeleton.  This  is  called 
the  cephalothorax.  Count  the  number  of  segments  in  the  abdomen  (the 
posterior  region).     This  number  is  constant  for  every  crayfish. 

The  shell  is  a  true  exoskeleton,  that  is,  it  is  formed  by  the  skin.     As  in 

the  exoskeleton  of  the  insects,  an  animal  material  called  chit  in  forms  the 

basis,  but  in  this  case  the  skeleton  is  strengthened  by  the  addition  of  lime. 

Test  a  piece  of  the  shell  with  acid.     What  results?     Is  anything  left 

*  For  full  laboratory  directions  see  Hunter  and  Valentine,  Manual,  page  121. 

91^ 


216 


ZOOLOGY 


behind  ?  What  is  this,  animal  or  mineral  matter  ?  Examine  the  shell  of  a 
dead  crayfish  and  try  to  find  out  how  the  segments  of  the  abdomen  are 
joined  together.  Notice  the  different  positions  taken  by  the  abdomen  in 
the  living  animal.     How  might  this  be  accounted  for  mechanically? 

The  small  appendages  attached  to  the  under  surface  of  the  segments  are 
called  the  swimmerets  or  pleopods.  How  many  are  attached  to  each  seg- 
ment? Observe  the  move- 
ment when  in  the  water.'  Why 
are  they  called  swimmerets? 
Notice  that  each  plcopod  is 
made  up  of  three  pieces,  a 
base  and  two  branches.  Now 
look  at  the  broad  appendage 
that,  together  with  the  last 
segment  of  the  abdomen, 
fcjrms  a  broad  finlike  appa- 
ratus, the  caudal  -fin.  You 
will  find  this  appendage  like- 
wise composed  of  three  pieces ; 
it  is  homologous  to  the  pleo- 
pods.  This  appendage  is 
known  as  the  uropod.  Cray- 
fish normally  swim  very  rap- 
idly in  a  backward  direction 
by  means  of  a  sudden  jerk- 
ing of  the  caudal  fin.  Other 
methods  of  locomotion  may 
be  observed  by  allowing  the 
animal  to  walk  in  a  shallow 
pan  with  a  little  water  in  it. 
Note  the  position  and  number 
of  jointed  legs  that  are  used 
in  locomotion.  Is  the  large 
pair  of  pincher  legs  used  for 
this  purpose?  If  so,  to  what 
extent  ?  Crayfish  have  a  defi- 
nite method  in  the  movement 
of  the  walking  legs,  the  first 
and  third  moving  in  alterna- 
tion with  the  second  and 
fourth  legs  on  the  same  side  of  the  animal.  Test  a  crayfish  to  see  if  this  rule 
holds  true.  Dp  you  find  any  other  methods  of  locomotion  than  the  ones 
mentioned? 

Watch  the  animal  in  its  movements  to  see  if,  in  avoiding  objects,  it  first 
allows  certain  parts  of  the  body  to  touch  the  object.  The  longer  of  the 
two  pairs  of  feelers  (the  antenna)  function  as  organs  of  touch.  Hairs 
which  are  sensitive  to  touch  are  also  found  in  various  other  parts  of  the 
bod3^  The  bases  of  the  antennse  are  broad,  and  a  small  flat  piece  projects 
outward  from  this  basal  portion.  The  antennae  are  believed  to  have  also 
the  function  of  smell.  Crayfish  are  thus  able  to  learn  of  the  presence  of 
food  at  a  considerable  distance  away.  The  short  appendages  immediately 
in  front  of  the  antennse  are  called  the  antennulce  (little  antennse).  Notice 
that  the  four  stalks  are  in  reality  two  branches  from  one  base  on  each 
side.  Part  of  this  appendage  is  believed  to  contain  the  organ  of  hearing. 
Test  in  any  manner  that  you  can  the  sight  of  the  crayfish.      Test  with 


1 

^^^1 

'^^^m 

■  .mi.,  w^- 

j-^-0^cm 

^^^^^^H 

Female  lobster,  showing  eggs  attached  to  the  swim- 
merets. From  photograph  loaned  by  the  American 
Museum  of  Natural  History. 


CRUSTACEANS 


217 


moving  objects  at  a  little  distance  and  then  close  to  the  animal.  You 
may  also  test  to  see  if  the  animal  can  distinguish  light  from  darkness.  This 
may  be  done  by  covering  half  of  the  tray  in  which  the  crayfish  is  con- 
fined. Then  place  the  animal  in  the  light  end  of  the  tray  to  see  if  it  will 
travel  toward  the  dark  end  of  the  tray.  This  may  be  repeated  by  placing 
the  animal  m  the  dark  end.  Thus  it  will  bo  possible  to  discover  the  reaction 
of  the  animal  to  the  light.  Notice  the  position  of  the  stalked  eyes.  Touch 
the  eye  with  a  pencil;  is  it  freely  movable?  In  what  direction?  Notice 
how  well  the  eye  is  protected  from  injury.  The  anterior  end  of  the  cara- 
pace projects  to  form  a  spiny  process;  this,  wn'th  the  socket  in  which  the 
eye  rests  and  its  position  on  the  side  of  the  head,  forms  ample  protection 


Mouth  parts  of  the  crayfish;  /.walking  appendage,  showing  attachraent  of  gill;  2,  the  jaw,  with 
palp;  3,  first  maxilla  (second  maxilla  not  shown);  4,  third  maxilliped;  5,  second  maxil- 
liped,  showing  baler;  6,  first  maxilliped,  showing  gill  attached;  7,  swimmeret;  5,  uropod. 

to  this  important  organ.  The  eyes  of  the  crayfish,  like  those  of  an  in- 
sect, are  compound.  They  differ  from  those  of  the  insect  in  being  borne 
on  stalks.  If  a  small  bit  of  the  exoskeleton  covering  the  eye  is  placed  un- 
der the  compound  microscope,  it  wall  be  found  to  be  made  up  of  a  num- 
ber of  little  rectangles;  this  shows  the  size  and  shape  of  a  surface  view  of 
the  units  composing  the  compound  eye. 

If  it  is  possible  to  have  the  aquarium  holding  the  crayfish  in  the  school- 
room, the  method  of  feeding  may  be  watched.  Notice  that  the  pincher  claws 
(chelipeds)  are  used  to  hold  and  tear  food,  as  well  as  for  defense  and  offense. 
Living  food  is  obtained  with  the  aid  of  the  chelipeds.  Food  is  shoved  by 
the  chelipeds  toward  the  mouth;  it  is  assisted  there  by  several  small  ap- 
pendages called  foot  jaws  (maxillipeds)  and  to  a  slight  degree  by  two  still 
smaller  paired  maxillce  just  under  the  maxillipeds.  Ultimately  the  food 
reaches  the  hard  jaws  and,  after  being  ground  between  them,  is  passed  down 
to  the  stomach.  If  you  hold  the  crayfish  in  such  a  position  that  you  can 
pour  a  little  beef  juice  or  other  edible  fluid  over  the  mouth  parts,  it  will  l>e 
possible  to  observe  the  mouth  parts  work  as  they  do  in  a  state  of  nature. 


218 


ZOOLOGY 


The  mouth  parts  of  a  crayfish  resting  in  the  aquarium  are  observed  to  be 
constantly  in  motion,  despite  the  fact  that  no  food  is  present.  If  the  crayfish 
is  taken  out  of  the  water  and  held  with  the  ventral  surface  upmost,  a  little 
carmine  (dissolved  in  water)  may  be  dropped  on  the  lower  surface  of  the 
animal.  This  carmine  runs  down  under  the  carapace.  If  now  the  animal 
is  held  in  water  in  the  same  position,  the  carmine  will  appear  from  both  sides 
of  the  mouth,  seemingly  propelled  by  something  which  causes  it  to  emerge 
in  little  puffs.  If  we  remove  the  maxillipeds  and  maxillse  from  a  dead 
specimen,  we  find  a  groove  leading  back  from  each  side  of  the  mouth  to  a 
cavity  of  considerable  size  on  each  side  of  the  body  under  the  carapace. 
This  is  the  gill  chamber.  It  contains  the  gills,  the  organs  which  take  oxygen 
out  of  the  water.  The  second  maxillae  are  prolonged  down  into  the  groove 
to  serve  as  bailers  or  scoops.  By  rapid  action  of  this  organ  a  current  of 
water  is  maintained  which  passes  over  the  gills. 

The  gills  are  outside  of  the  body,  although  protected  by  the  carapace.  If 
the  carapace  is  partly  removed  on  one  side,  they  will  be  found,  looking  some- 
what like  white  feathers.  The  blood  of  the  crayfish  passes  by  a  series  of 
vessels  into  the  long  axis  of  the  gill;  in  this  organ  the  blood  tubes  divide  into 
very  minute  tubes,  the  walls  of  which  are  extremely  delicate.  Oxygen,  dis- 
solved in  the  water,  passes  into  the  blood  by  osmosis,  during  which  process 
the  blood  loses  some  carbon  dioxide.  Notice  that  the  gills  are  kept  from 
drying  by  being  placed  in  a  nearly  closed  chamber,  which  is  further  adapted 
to  its  function  by  means  of  the  row  of  tiny  hairs  which  border  the  lower 
edge  of  the  carapace. 


Crayfish  with  the  left  half  of  the  body  structures  removed;  a,  intestine;  6,  ventral  artery; 
c,  brain;  e,  heart;  et,  gastric  teeth;  i,  oviduct;  Z,  digestive  gland;  m,  muscles;  n,  green 
gland  (kidney);  o,  ovary;  p,  pyloric  stomach;  r,  nerve  cords;  s,  cardiac  stomach; 
si,  mouth;  w,  telson;  w,  openings  of  veins  into  the  pericardial  sinus.  Twice  natural  size. 
Davison,  Zoology. 

The  laboratory  exercise  should  conclude  with  a  drawing  of  the  animal 
from  the  side,  about  natural  size,  with  part  of  the  carapace  cut  away  to 
show  the  gills.  Show  as  many  of  the  above-mentioned  parts  as  possible. 
For  other  useful  drawings  see  Hunter  and  Valentine,  Manual,  page  124. 

Circulation.  —  The  circulation  of  blood  in  the  crayfish  takes  place  in  a 
system  of  thin-walled,  flabby  vessels  which  are  open  in  places,  allowing  the 
blood  to  come  in  direct  contact  with  the  tissues  to  w^hich  it  flows.  The 
heart  lies  on  the  dorsal  side  of  the  body,  inclosed  in  a  delicate  bag,  into 
which  all  the  blood  in  the  body  eventually  finds  its  way  during  its  circulation. 


CRUSTACEANS  219 

Digestion.  —  Food  which  is  not  ground  up  into  pieces  smah  enough  for 
the  purpose  of  digestion  is  still  further  masticated  by  means  of  three  teeth, 
strong  projections,  one  placed  on  the  midline  and  two  on  the  side  walls  of 
the  stomach.  The  exoskeleton  of  the  crayfish  extends  down  into  the 
stomach,  thus  forming  the  gastric  mill  just  described. 

The  stomach  is  divided  into  anterior  and  posterior  parts  separated  fioni 
each  other  by  a  constriction.  The  posterior  part  is  lined  with  tiny  pro 
jections  from  the  wall  which  make  it  act  as  a  strainer  for  the  food  passing 
through.  Thus  the  unbroken  particles  of  food  are  kept  in  the  anterior  end 
of  the  stomach.  Opening  into  the  posterior  end  of  the  stomach  are  two 
large  digestive  glands  which  further  prepare  the  food  for  absorption  through 
the  walls  of  the  intestine.  Once  in  the  blood,  the  fluid  food  is  circulated 
through  the  body  to  the  tissues  which  need  it. 

Nervous  System.  —  The  internal  nervous  system  of  a  crayfish  consists  of 
a  series  of  collections  of  nerve  cells  {ganglia)  connected  by  means  of  a 
double  line  of  nerves.  Posterior  to  the  gullet  this  chain  of  ganglia  is  found 
on  the  ventral  side  of  the  body,  near  the  body  wall.  It  then  encircles  the 
gullet  and  forms  a  brain  in  the  head  region,  the  latter  formed  from  several 
ganglia  which  have  grown  together.  From  each  of  the  ganglia,  nerves  pass 
off  to  the  sense  organs  and  into  the  muscles  of  the  body.  These  nerve 
fibers  are  of  two  sorts,  those  bearing  messages  from  the  outside  of  the  body 
to  the  central  nervous  system  (these  messages  result  in  sensations),  and 
those  which  take  outgoing  messages  from  the  central  nervous  system  (motor 
impulses),  w^hich  result  in  muscular  movements. 

Development.  —  The  sexes  in  the  crayfish  are  distinct.  The  developing 
eggs,  which  are  provided  with  a  considerable  supply  of  food  material,  are 
glued  fast  to  the  swimmerets  of  the  mother,  and  there  develop  in  safety. 
The  young,  when  they  first  hatch,  remain  clinging  to  the  swimmerets  for 
several  weeks. 

Excretion  of.  Wastes.  —  On  the  basal  joint  of  the  antennae  are  found 
two  projections,  in  the  center  of  which  are  found  tiny  holes.  These  are  the 
openings  of  the  green  glands,  organs  which  have  the  function  of  the  elimina- 
tion of  nitrogenous  waste  from  the  blood,  the  function  of  the  human  kidneys. 

Characters  of  Crayfish  and  its  Allies.  —  Our  study  of  crayfish  shows 
us  that  animals  belonging  to  the  same  group  as  itself  have  several 
well-marked  characteristics.  The  most  important  are  the  presence 
of  a  segmented  limy  exoskeleton,  gills,  jointed  appendages,  a  pair 
to  each  segment  of  the  body  (except  the  last) ;  and,  as  we  shall  see 
later,  they  pass  through  a  metamorphosis  or  change  of  form  before 
they  reach  the  adult  state.  We  find  that  the  Crustacea  fall 
naturally  into  two  classes,  those  in  which  the  number  of  pairs  of 
appendages  is  indefinite,  and  those  in  which  the  number  is  fixed 


220 


ZOOLOGY 


at  nineteen.     In  this  latter  class  are  placed  the  crayfish,  lobster, 
blue  crab,  shrimp,  and  most  of  our  common  crustaceans. 

The  North  American  Lobster.  —  In  structure  it  is  almost  the 
counterpart  of  its  smaller  cousin,  the  crayfish.  Its  geographical 
range  is  a  strip  of  ocean  bottom  along  our  coast,  estimated  to 

vary  from  thirty  to  fifty  miles  in  width. 
This  strip  extends  from  Labrador  on 
the  north  to  Delaware  on  the  south. 
The  lobster  is  highly  sensitive  to 
changes  in  temperature.  It  migrates 
from  deep  to  shallow  water  or  vice 
versa  according  to  the  temperature  of 
the  water,  which  in  winter  is  relatively 
warmer  in  deep  water  and  cooler  in 
shallows.  Sudden  changes  in  the 
water  of  a  given  locality  may  cause 
them  to  disappear  from  that  place. 
The  more  abundant  food  supply  near 
the  shore  also  aids  in  determining 
the  habitat  of  the  lobster.  Lobsters 
do  not  appear  to  migrate  north  and 
south  along  the  coast.  While  little  is 
known  about  their  habits  on  the  ocean 
bottom,  it  is  thought  that  they  con- 
struct burrows  somewhat  like  the  cray- 
fish, in  which  they  pass  part  of  the 
time.  As  they  have  the  color  of  the 
bottom  and  as  they  pass  much  of  their  time  among  the  weed- 
covered  rocks,  they  are  able  to  catch  much  living  food,  even 
active  fishes  falling  prey  to  their  formidable  pinchers.  They  move 
around  freely  at  night,  usually  remaining  quiet  during  the  day, 
especially  when  in  shallow  water.  They  eat  some  dead  food;  and 
thus,  like  the  crayfish,  they  are  scavengers. 

Development.  —  The  female  lobsters  begin  to  lay  eggs  when 
about  seven  inches  in  length.  Lobsters  of  this  size  lay  in  the 
neighborhood  of  five  thousand  eggs;  this  number  is  increased  to 
about  ten  thousand  in  lobsters  of  moderate  size  (ten  inches  m 


North  American  Lobster.  This 
specimen,  preserved  at  the  U.S. 
Fish  Commission,  was  of  un- 
usual size  and  weighed  over 
twenty  pounds.  Notice  the 
chelipeds. 


CRUSTACEANS 


221 


length) ;  in  exceptionally  large  specimens  as  many  as  one  hundred 
thousand  eggs  are  sometimes  laid.  The  eggs  are  laid  every  alter- 
nate year,  usually  during. the  months  of  July  and  August.  Eggs 
laid  in  July  or  August,  as  shown  by  observations  made  along  the 
coast  of  Massachusetts,  hatch  the  following  May  or  June.  The 
eggs  are  provided  with  a  large  supply  of-  yolk  (food),  the  develop- 
ment of  the  young  animal  taking  place  at  the  expense  of  this  food 
material.  After  the  young  escape  from  the  egg  they  are  almost 
transparent  and  little  like  the  adult  in  form.  During  this  period 
of  their  lives  the  mortality  is  very- 
great,  as  they  are  the  prey  of  many 
fish  and  other  free-swimming  ani- 
mals. It  is  estimated  that  barely 
one  in  five  thousand  survdves  this 
period  of  peril.  At  this  time  they 
grow  rapidly,  and  in  consequence 
are  obliged  to  shed  their  exoskele- 
ton  (molt)  frequently.  During  the 
first  six  weeks  of  life,  when  they 
swim  freely  at  the  surface  of  the 
water,  they  molt  from  five  to  six 
times.^ 

Molting.  —  During  the  first  year 
of  its  life  the  lobster  molts  from 
fourteen  to  seventeen  times.  Dur- 
ing this  period  it  attains  a  length  of  from  two  to  three 
inches.  Molting  is  accomplished  in  the  following  manner:  The 
carapace  is  raised  up  from  the  posterior  side  and  the  body  then 
withdrawn  through  the  opening  between  it  and  the  abdomen. 
The  most  wonderful  part  of  the  process  is  the  withdrawal  of  the 
flesh  of  the  large  claws  through  the  very  small  openings  which 
connect  the  limbs  with  the  body.  The  blood  is  first  withdrawn 
from  the  appendage ;  this  leaves  the  flesh  in  a  flabby  condition  (a 

^  Recent  economic  investigations  upon  the  care  of  the  young  developing  lobster 
show  that  animals  protected  during  the  first  few  months  of  free  existence  have 
a  far  better  chance  of  becoming  adults  than  those  left  to  grow  up  without  protec- 
tion. Later  in  life  they  sink  to  the  bottom,  and  because  of  their  protectively 
colored  shell  and  the  habit  of  hiding  under  rocks  and  in  burrows,  they  are  com- 
paratively safe  from  the  attack  of  eneroies. 


Metamorphosis  of  a  shrimp;  a,  naupliiis 
or  earliest  stage;  h,  c,  d,  later  larval 
stages;  e,  adult.  Note  that  as  the 
animal  grows  more  appendages  ap- 
pear, and  that  these  develop  backward 
from  the  anterior  end. 


222 


ZOOLOGY 


state  similar  to  the  taproot  which  has  lost  water  by  osmosis)  so 
that  the  muscles  can  be  drawn  through  without  injury.  The 
lobster  also  molts  a  part  of  the  lining  of  the  digestive  tract  as 
far  as  the  posterior  portion  of  the  stomach.  Immediately  after 
molting  the  lobster  is  in  a  helpless  condition,  and  is  more  or  less 
at  the  mercy  of  its  enemies  until  the  new  shell,  which  is  se- 
creted by  the  skin,  has  grown.  This  process  takes  several  weeks 
to  complete. 

Economic  Importance.  —  The  lobster  is  highly  esteemed  as 
food,  and  is  rapidly  disappearing  from  our  coasts  as  the  result  of 
overfishing.  Between  twenty  million  and  thirty  million  are  yearly 
taken  on  the  North  Atlantic  coast.  This  means  a  value  at  present 
prices  of  about  $15,000,000.  Laws  are  now  enacted  in  New  York 
and  other  states  against  overfishing.  Egg-carrying  lobsters  must 
be  returned  to  the  water,  all  smaller  than  six  to  nine  inches  in 
length  (the  law  varies  in  different  states)  must  be  put  back;  other 
restrictions  are  placed  upon  the  taking  of  the  animals,  in  hope  of 
saving  the  race. from  extinction.  Some  states  now  hatch  and  care 
for  the  young  for  a  period  of  time;  the  United  States  Fish  Com- 
mission is  also  doing  much  good  work,  in  hope  of  restocking  to 
some  extent  the  now  almost  depleted  waters. 

Shrimps.  —  Several  other  common  crustaceans  are  near  relatives 
of  the  crayfish.  Among  them  are  the  shrimps  and  prawns,  thin- 
shelled,  active  crustaceans  common  along  our  eastern  coast.  In 
spite  of  the  fact  that  they  form  a  large  part  of  the  food  supply  of 
many  marine  animals,  especially  fishes,  they  do  not  appear  to  be 

decreasing  in  numbers.  Be- 
sides this  value  as  a  food, 
they  are  also  used  by  man, 
the  shrimp  fisheries  in  this 
country  aggregating  almost 
$1,000,000  yearly. 

The  Blue  Crab.  — Another 
edible  crustacean  of  consid- 
erable economic  importance 
is  the  blue  crab.  Crabs  are 
found  inhabiting  muddy  bot- 


The  edible  blue  crab.     From  photograph  loaned 
by  the  American  Museum  of  Natural  History. 


CRUSTACEANS 


223 


toms;  in  such  localities  they  are  caught  in  great  numbers  in 
nets  or  traps  baited  with  decaying  meat.  They  are,  indeed, 
among  our  most  valuable  sea  scavengers,  although  they  are  car- 
nivorous hunters  as  well.  The  body  of  the  crab  is  short  and  broad, 
being  flattened  dorso-ventrally.  The  abdomen  is  much  reduced 
in  size.  Usually  it  is  carried  close  to  the  under  surface  of  the 
cephalothorax ;  in  the  female  the  eggs  are  carried  under  its  ventral 
surface,  fastened  to  the  rudimentary  swimmerets.  The  young 
crabs  differ  considerably  in  form  from  the  adult.  They  undergo 
a  complete  metamorphosis 
(change  of  form),  and  their 
method  of  life  differs  from  the 
adult.  Immediatelv  after 
molting,  crabs  are  greatly 
desired  by  man  as  an  article 
of  food.  They  are  then  known 
as  ''shedders,"  or  soft-shelled 
crabs. 


The  fiddler  crab.     From  photograph  loaned  by 
the  American  Museum  of  Natural  History. 


Other  Crabs.  —  Other  crabs  seen  along  the  New  York  coast  are  the 
prettily  colored  lady  crabs,  often  seen  running  along  our  sandy  beaches  at 
low  tide;  the  fiddler  crabs,  interesting  because  of  their  burrows  and  gre- 
garious habits;  and  perhaps  most  interesting  of  all,  the  hermit  crabs. 
The  hermit  crabs  use  the  shells  of  snails  as  homes.     The  abdomen  is  soft, 

and  unprotected  by  a  limy  exoskeleton, 
and  has  adapted  itself  to  its  conditions 
by  curling  around  in  the  spiral  snail 
shell,  so  that  it  has  become  asym- 
metrical. These  tiny  crabs  are  great 
fighters  and  wage  frequent  duels  with 
each  other  for  possession  of  the  more 
desirable  shells.  They  exchange  their 
borrowed  shells  for  larger  ones  as  growth 
forces  them  from  their  first  homes. 

The  habits  of  these  animals,  and  those 
of  the  fiddler  crabs,  might  be  studied 
with  profit  by  some  careful  boy  or  girl 
who  spends  a  summer  at  the  seashore 
and  has  the  time  and  inclination  to 
devote  to  the  work.  Of  especial  interest 
would  be  a  study  of  the  food  and  feeding  habits  of  the  fiddler  crabs. 


Hermit  crab,  about  twice  natural  size. 
From  photograph  loaned  by  the 
American  Museum  of  Natural 
History. 


224 


ZOOLOGY 


A  deep-water  crab  often  seen  along  Long  Island  Sound  is  the  spider  crab, 
or  sea  spider  as  it  is  incorrectly  called  by  fishermen.  This  animal,  with  its 
long  spiderlike  legs,  is  neither  an  active  runner  or  swimmer;  it  is,  however, 
protectively  colored  like  the  dark  mud  and  stones  over  which  it  crawls.  The 
resemblance  to  the  bottom  is  further  heightened  by  the  rough  body  covering, 
which  gives  a  hold  for  seaweeds  and  sometimes  sessile  animals,  as  barnacles, 
hydroids,  or  sea  anemones,  to  fasten  themselves. 

A  spider  crab  from  the  Sea 
of  Japan  is  said  to  be  the 
largest  crustacean  in  the  world, 
specimens  measuring  eighteen 
feet  from  tip  to  tip  of  the  first 
pair  of  legs  having  been  found. 

Symbiosis.  —  Certain  of 
the  spider  crabs,  as  well 
as  some  of  the  larger  deep- 
water  hermit  crabs,  have 
come  to  live  in  a  relation 
of  mutual  helpfulness  with 
hydroids,  sponges,  and  sea 
anemones.  These  animals 
attach  themselves  to  the 
shell  of  the  crab  and  are 
carried  around  by  it,  thus 
receiving  a  constant 
change  of  position  and 
a  supply  of  food.  What  they  do  for  the  crab  in  return  is  not 
so  evident,  although  one  large  Chinese  hermit  regularly  plants  a 
sea  anemone  on  its  big  claw;  when  forced  to  retreat  into  its  shell, 
the  entrance  is  thus  effectually  blocked  by  the  anemone.  The 
living  of  animals  in  a  mutually  helpful  relation  is  called  symbiosis. 
Of  this  we  have  already  had  some  examples  in  plants  as  well  as 
among  animals.     (See  Lichens,  page  172.) 

Habitat.  —  Most  crustaceans  are  adapted  to  live  in  the  water; 
a  few  forms,  however,  are  found  living  on  land.  Such  are  the 
wood  lice,  the  pill  bugs,  which  have  the  habit  of  rolling  up  into  a 
ball  to  escape  attack  of  enemies,  the  beach  fleas,  and  others.  The 
cocoanut  crab  of  the  tropics  climbs  trees  in  search  of  food,  return- 
ing to  the  water,  at  intervals,  to  moisten  the  gills. 


Giant  spider  crab  from  Japan.     From  photograph 
loaned  by  the  American  Museum  of  Natural  History. 


CRUSTACEANS 


225 


Classification.  —  All  the  forms  of  crustaceans  mentioned  belong  to 
that  subclass  of  crustaceans  called  the  Malacostraca,  the  characters 
of  the  group  being  a  definite  number  of  segments  and  appendages. 
All  having  five  pairs  of  walking  appendages  are  called  decapods. 
How  many  of  the  above-mentioned  forms  are  decapods? 


Entomostraca.  —  Another  subclass  qf  crustaceans,  in  which  the  number 
of  appendages  is  not  fixed,  is  the  group  Entomostraca.  They  arc  mostly 
small  animals,  some  species  existing  in  countless  numbers.  Such  are  the 
fairy  shrimps  found  appearing  in  early  spring  in  fresh-water  ponds,  little 
translucent  swimming  forms  from  one  half  to 
three  fourths  of  an  inch  in  length.  Another 
fresh-water  form  often  seen  in  aquaria  is  the 
water  flea  (Daphnia).  From  the  economic  stand- 
point, probably  the  most  important  crustaceans 
that  we  shall  study  are  the  copepods.  These 
tiny  animals  are  barely  visible  to  the  naked  eye. 
They  are  found  in  almost  every  part  of  the 
world,  from  the  arctic  seas  to  those  of  the  tropics, 
and  in  fresh  as  well  as  salt  water.  They  are 
so  numerous  that  the  sea  in  places  is  colored 
by  their  bodies.  So  prolific  are  they  that  it  is 
estimated  that  one  copepod  may  produce  in  a 
single  year  four  billion  five  hundred  million 
offspring.  These  animals  form  a  large  part  of 
the  food  supply  of  many  of  our  most  important 
food  fishes  as  well  as  the  food  of  many  other 
aquatic  animals.  They  are,  then,  in  an  indirect 
way,  of  immense  economic  value. 

Degenerate  Crustaceans.  —  One  of  the  most 
interesting  forms  to  a  zoologist  is  the  goose  bar- 
nacle. This  crustacean  is  free-swimming  during  its  early  life.  Later, 
however,  after  passing  through  several  changes  in  form  during  its  de- 
velopment, the  barnacle  settles  down  on  a  rock  or  some  floating  object, 
fastens  itself  along  the  dorsal  surface,  and  remains  so  fastened  during  the 
rest  of  its  Kfe.  Food  comes  to  it  in  a  current  of  water,  which  is  set  in 
motion  by  the  rhythmical  beating  of  the  appendages.  Thus  food  particles 
are  carried  along  the  ventral  side  of  the  body  to  the  mouth.  Such  animals 
are  said  to  be  degenerate. 

Parasitic  Crustaceans. — Other  crustaceans  have  become  even  more  help- 
less and  have  come  to  take  their  hving  from  other  animals.  In  some  cases 
they  are  simply  a  bag  for  absorbing  nourishment  from  the  host  on  which 
they  are  fastened.     Such  is  the  Sacculina,  a  degenerate  crustacean  that  Hves 

hunter's   BIOL, 16 


Cyclops,  a  common  cope- 
pod,  enlarged  about 
twenty  times.  A  mass 
of  eggs  at  the  right. 


226 


ZOOLOGY 


Group  of  acorn  barnacles  (closed),  with  starfish 
moving  over  the  mass.  Each  shell  contains  a 
fixed,  degenerate  crustacean. 


attached  to  the  body  of  the 
crab.  Others  attach  them- 
selves to  fishes  and  are  known 
to  fishermen  as  fish  Hce. 

Characters  Common  to 
all  Crustaceans.  —  In  spite 
of  all  the  differences  in 
structure  found  in  the  va- 
rious crustaceans  studied, 
there  are  a  number  of  char- 
acters possessed  by  all 
crustaceans  in  common. 
They  have  a  segmented 
body  covered  with  an  exo- 
skeleton;  the  latter  con- 
tains chitin  and  carbonate  of  lime.  The  body  is  bilaterally  sym- 
metrical (except  in  the  hermit  crab).  The  appendages  are  jointed 
and  branched.  Two  pairs  of  antennae  are  present.  The  eyes  are 
stalked  and  compound.  Crustaceans  breathe  by  means  of  gills 
and  are  mostly  aquatic. 

Reference  Books 
for  the  pupil 

Burnet,  School  Zoology,  pages  67-73.     American  Book  Company. 

Davison,  Practical  Zoology,  pages  133-141.     American  Book  Company. 

Herrick,  Text-book  in  General  Zoology,  Chap.  XIII.     American  Book  Company. 

Jordan,  Kellogg,  and  Heath,  Animal  Studies,  Chap.  IX.  D.  Appleton  and  Com- 
pany. 

Hunter  and  Valentine,  Laboratory  Manual  of  Biology,  pages  138-146.  Henry  Holt 
and  Company. 


FOR    THE    TEACHER 


Herrick,   The  American  Lobster.     Report  of  U.S.   Fish  Commission,   1895. 

Parker,  Elementary  Biology.     The  Macmillan  Company. 

Parker  and  Haswell,  Text-book  of  Zoology.     The  Macmillan  Company. 


XIX.     INSECTS 

Insects  and  Crustaceans  Compared.  —  Both  crustaceans  and 
insects  belong  to  a  great  group  of  animals  which  agree  in  that 
they  have  jointed  appendages  and  bodies,  and  that  they  possess 
an  exoskeleton.     This  group  is  known  as. the  Art/iropoda. 

Insects  differ  structurally  from  crustaceans  in  having  three 
regions  in  the  body  instead  of  two.  The  number  of  legs  (three 
pairs)  is  definite  in  the  insects ;  in  the  crustaceans  the  number  some- 
times varies  (as  in  the  Entomostraca),  but  is  ahvays  more  than 
three  pairs.  The  exoskeleton,  composed  wholly  of  chitin  in  the 
insects,  is  usually  strengthened  with  lime  in  the  crustaceans.  Both 
groups  have  compound  eyes,  but  those  of  the  Crustacea  are  stalked 
and  movable.  The  crustaceans  receive  sensations  of  touch  by 
means  of  sensory  hairs  which  protrude  from  the  exoskeleton.  The 
other  sense  organs  do  not  differ  greatly.  The  most  marked  differ- 
ences are  physiological.  The  crustaceans  take  in  oxygen  from  the 
water  by  means  of  gills,  while  the  insects  are  air  breathers,  using 
for  this  purpose  air  tubes  called  tracheoe. 

The  young  of  both  insects  and  crustaceans  usually  undergo 
several  changes  in  form  before  the  adult  stage  is  reached. 
They  are  thus  said  to  pass  through  a  metamorphosis.  Both 
insects  and  crustaceans,  because  of  their  exoskeleton,  must 
molt  in  order  to  increase  in  bulk. 

The  insects  are  divided  into  a  number  of  large  groups  called 
orders.  The  insects  found  in  each  order  possess  certain  char- 
acters in  common.  We  shall  now  examine  several  representatives 
from  some  of  the  different  orders  of  insects  commonly  met  with. 

The   Order   Orthoptera 

The  Locust.  —  The  locust  or  short-horned  grasshopper  is  a 
type  of  the  class  Insecta,  which  is  characterized  by  possessing  a 

227 


228 


ZOOLOGY 


body  made  up  of  segments,  having  jointed  appendages,  three 
pairs  of  legs,  and  breathing  through  a  system  of  air  tubes  called 

trachece.  It  also  belongs 
to  the  order  Orthoptera 
(straight  wings)  because 
the  hind  wings,  when  at 
rest,  lie  folded  up  length- 
wise close  to  the  body. 


Locust  (red-legged  grasshopper);  Ah,  abdomen;  Ant., 
antennae;  E,  eye;  M,  mouth;  P,  pads  on  feet; 
T,  thorax. 


External  Structure}  —  Any 
common  form,  as  Melanoplus 
femur-rubrum ,  may  be  used. 
Examine  the  body  of  the  grass- 
hopper. The  anterior  region 
is  the  head,  the  middle  part 
the  thorax,  the  posterior  the 
abdomen.  To  which  region 
are  wings  and  legs  attached? 
Which  region  is  the  stoutest? 
Notice  that  the  body  is  covered  with  an  exoskeleton.  This  is  composed  of 
chitin,  a  substance  chemically  akin  to  that  of  a  cow's  horn. 

The  grasshopper  makes  its  home  in  fields  of  grass.  Some  species  live  in 
vacant  lots  where  there  is  considerable  earth  exposed.  Do  such  grass- 
hoppers ever  have  the  color  of  their  surroundings  ?  How  might  this  be  of 
service  to  them? 

Examine  the  legs  of  a  living  grasshopper,  with  a  view  to  finding  out  their 
position  when  at  rest.  Examine  the  hind  legs.  Do  you  find  any  adapta- 
tions present  which  fit  the  legs  for  jumping  ?  Examine  the  hooks  and  pads 
on  the  last  segment  or  tarsus.  Look  for  other  adaptations.  Besides  flying 
and  hopping,  the  grasshopper  also  crawls.  In  a  resting  position,  it  clings  by 
means  of  the  hooks  and  pads  on  the  foot  or  tarsus. 

Spread  out  the  wings.  Note  their  position.  Note  any  differences  between 
the  two  pairs.  Which  pair  would  be  most  useful  in  flight?  Notice  the  deli- 
cate lacelike  underwings,  the  supporting  veins  of  which  are  composed  of 
tubes  that  carry  blood  and  air. 

Notice  the  alDdomen  carefully.  The  most  anterior  segment  is  incomplete, 
and  bears  an  oval  structure,  the  tympanum,  or  ear  drum.  Count  the  number 
of  complete  segments  in  the  abdomen.  The  female  grasshopper  has  the 
free  end  of  the  abdomen  modified  for  the  purpose  of  egg  laying.  Note  the 
two-parted  structures  making  up  the  ovipositor  or  egg  layer.  The  male 
has  a  more  rounded  abdomen. 

Observation  of  the  abdomen  of  a  living  grasshopper  shows  a  frequent 
movement  of  the  abdomen.  Count  the  number  of  movements  in  a  minute. 
This  is  the  breathing  of  the  grasshopper.  Along  the  side  of  the  abdomen 
in  eight  of  the  segments  (in  the  red-legged  grasshopper)  are  found  tiny 
openings  called  spiracles.  A  large  spiracle  may  easily  be  found  in  the  middle 
segment  of  the  thorax.  These  spiracles  open  into  little  tubes  called  tracheae. 
The  tracheae  carry  air  to  all  parts  of  the  body.  By  the  movements  of  the 
abdomen  just  noted,  air  is  drawn  into  and  forced  out  of  the  tracheae. 


*  For  laboratory  directions  see  Hunter  and  Valentine,  Manual,  page  101. 


INSECTS 


229 


Spiracle  with  its  trachea}  removed  from  an 
insect;  s,  spiracle.  Three  times  natural 
size.    Photographed  by  Davison. 


Tracheae.— The  trachese  divide  and  subdivide  like  branches  of 
a  tree  so  that  all  the  body  cavity  is  reached  by  their  fine  endings. 
Some  even  pass  outward  into  the 
veins  of  the  wings.  Each  of 
these  tubes  contains  air.  The 
blood  of  an  insect  does  not  cir- 
culate through  a  system  of  closed 
blood  tubes  as  in  man,  but  in- 
stead it  more  or  less  completely 
fills  that  part  of  the  body  cavity 
which  is  not  filled  with  other 
organs.  A  heart  (a  hollow  mus- 
cular organ  containing  several 
openings,  situated  on  the  dorsal 
side  of  the  insect)  causes  move- 
ment of  the  blood  inside  the  body 
cavity  in  much  the  same  way 
that  a  rubber  bulb  would  circu- 
late water  if  squeezed  inside  a 
pail  of  water,  so  that  sooner  or  later  the  blood  comes  in  contact 
with  the  oxygen  passed  in  through  the  trachese. 

Muscular  activity.  —  Insects  have  the  most  powerful  muscles  of 
any  animals  of  their  size.  Relatively,  an  enormous  amount  of 
energy  is  released  during  the  jumping  or  flying  of  a  grasshopper. 
The  tracheae  pass  directly  into  the  muscles,  where  oxidation  takes 
place  when  the  muscles  are  exercised.  Thus  oxygen  is  taken 
directly  to  the  parts  of  the  body  where  it  is  to  be  used.  The  body 
temperature  of  the  grasshopper  is  slightly  higher  than  the  sur- 
rounding air.     Why? 

Mouth  Parts.  —  Feed  a  grasshopper  with  a  blade  of  grass.  Note  how  the 
animal  holds  the  grass.  What  appendages  aro  used  ?  Note  the  upper  lip  and 
lower  lips,  the  latter  biparted.  The  dark  brown  Jaws  (mandibles)  may  be 
seen  underneath.  Below  them  are  a  pair  of  smaller  pointed  parts,  the 
maxillse,  to  which  are  attached  a  pair  of  jointed  palps.  Note  also  that  palps 
are  attached  to  the  lower  lip. 

Food  Taking  and  Blood  Making.  —  The  plant  food  taken  by  the 
grasshopper  is  held  in  place  in  the  mouth  by  means  of  the  little 
jaws  or  maxillse  while  it  is  cut  into  small  pieces  by  the  mandibles. 


230  ZOOLOGY 

Just  behind  the  mouth  is  a  large  crop  into  which  empty  the  con^ 
tents  of  the  saUvary  glands.  It  is  this  fluid  mixed  with  digested 
food  that  we  call  the  "  grasshopper's  molasses."  After  the  food 
is  digested  by  the  action  of  the  saliva  and  other  juices,  it  passes 
in  a  fluid  state  through  the  walls  of  the  intestine  where  most  of 
it  becomes  part  of  the  blood.  As  blood  it  is  passed  on  to  tissues, 
such  as  muscle,  to  be  used  in  repairing  that  which  is  used  up 
during  the  flight  of  the  insect.  Some  of  the  foods  are  doubtless 
at  once  oxidized  to  release  energy  for  the  active  insect. 

Eyes.  —  A  considerable  part  of  the  surface  of  the  head 
of  the  grasshopper  is  taken  up  by  the  compound  eyes. 
Compare  them  with  your  own  in  position.  Examination 
with  a  lens  shows  the  whole  surface  to  be  composed  of 
tiny  hexagonal  spaces  called  facets.  Each  facet  is  be- 
lieved to  be  a  single  eye,  with  perhaps  distinct  vision 
from  its  neighbor.  The  grasshopper  also  has  three  simple 
eyes  on  the  front  of  the  head.     Find  them. 

Other    Sense    Organs. —  The    segmented   feelers   or 

antennoe  have  to  do  with  the  sense  of  touch  and  smell. 

The  ear  of  the  grasshopper  is  found  under  the  wing  on 

the  first  segment  of  the  abdomen  as  before  noted.     Cov- 

T        t  d"    \      f      ^ring  the  body  and  on  the  appendages,  are  found  hairs 

of    part    of   the  (sensory  hairs)  which  appear  to  be  sensitive  to  touch. 

compound  eye  of        Nervous  System.  —  The  nerve  chain,  as  in  the  cray- 

fe^ets^c!  nerves',  ^^h,  is  on  the  ventral  side  of  the  body.    As  in  the  crayfish, 

it  passes  around  the  gullet  near  the  head  to  the  dorsal  side, 

where  a  collection  of  ganglia  forms  the  brain.      Nerves  leave  the  central 

system  as  outgoing  fibers  which  bear  motor  impulses.      Other  nerve  fibers 

pass  inward,  and  produce  sensations. 

Make  a  careful  drawing  of  the  locust,  showing  as  many  of  the  above  parts 
as  you  can,  and  label  them  neatly. 

Life  History.  —  The  female  red-legged  locust  lays  its  eggs  by 
digging  a  hole  in  the  ground  with  its  ovipositor  or  egg  layer,  the 
modified  end  of  the  abdomen.  From  twenty  to  thirty  eggs  are 
laid  in  the  fall;  these  hatch  out  in  the  spring  as  tiny  wingless 
grasshoppers,  otherwise  like  the  adult.  As  in  the  crayfish,  the 
young  molt  in  order  to  grow  larger,  each  grasshopper  under- 
going several  molts  before  reaching  the  adult  state.  In  the  fall 
most  of  the  adults  die,  only  a  few  surviving  the  winter. 

Economic  Importance  of  the  Grasshopper.  —  As  far  back  as 
Biblical   times,  the  grasshopper  was  noted  for   its  destructive- 


INSECTS 


231 


ness.  Frequent  mention  has  been  made  of  damage  wrought  by 
them  in  the  early  history  of  this  country.  In  recent  times,  the 
damage  has  been  appalling,  especially  in  the  central  West.  In 
1874-1876  the  damage  to  crops  by  the  Rocky  Mountain  locust 
has  been  estimated  at  $200,000,000.  At  certain  times,  these 
locusts  migrate  from  Colorado,  Wyoming,  and  Dakota,  where  they 
breed  during  the  summer,  and  descend  in  countless  millions  upon 
the  grain  fields  to  the  eastward.  Fortunately  these  invasions 
have  been  rare. 

Relatives  of  the  Locust.  —  One  member  of  this  group  that  we 
associate  with  the  grasshopper  is  the  cricket.  In  structure  and 
life  habits  it  resembles  the  locust.  Crickets  live  most  of  the 
time  under  logs  or  stones,  and  seem  to  prefer  darkness  to  light. 
The  cheerful  chirp  of  the  male  house  cricket  is  made  by  rubbing 
the  thickened  edge  of  one  wing  against  a  rasplike  projection  on  the 
opposite  wing.  The  rate  of  the 
chirp  seems  to  depend  upon 
the  temperature  of  the  sur- 
rounding air.  Another  musi- 
cian known  to  all  is  the  katy- 
did. This  insect,  with  its  green 
body  and  wings,  can  scarcely 
be  distinguished  from  the 
leaves  on  which  it  rests.  This 
affords  the  katydid  immunity 
from  attack  by  many  enemies. 
The  protection  thus  received 
illustrates  what  is  called  protec- 
tive resemblance.  The  walking 
stick,  which  resembles  the 
twigs  on  which  it  is  found, 
and  the  walking  leaf  insect 
of  the  tropics,  are  other  ex- 
amples of  protective  resem- 
blance. 

The  mantis,  shown  in  the  illustration  on  the  following  page,  is 
provided  with  strongly  built  forelegs,  with  which  it  seizes  and 


The  walking  stick  on  twig,  showing  protective 
resemblance. 


232 


ZOOLOGY 


*  ^^^^ff 

\ 

^ 

1  ' 

i' 

4 

Mantis,  showing  aggressive 
resemblance. 


holds  insects  on  which  it  preys.  The 
mantis  has  the  color  of  its  immediate 
surroundings,  and  is  thus  enabled  to 
seize  its  prey  before  the  latter  is  aware 
of  its  presence.  This  is  known  as  a 
case  of  aggressive  resemblance,  because 
by  means  of  its  likeness  to  its  sur- 
roundings the  animal  is  enabled  to 
attack  its  prey  more  easily. 

The   Order   Lepidoptera 

The  Monarch  Butterfly.^  —  The  body 
of  the  butterfly,  as  that  of  the  grass- 
hopper, is  composed  of  three  regions. 
This  division  of  the  body  is  charac- 
teristic of  all  insects. 

Compare  with  the  grasshopper  as  to  the 
number  and  comparative  size  of  the  legs. 
Notice  that  the  first  pair  is  so  short  that 
Compare  the  wings  with  those  of  the  grass- 
Wliich  insect  probably  has  the  best  powers 


they  are  not  used  for  walking, 
hopper  as  to  size  and  shape, 
of  flight? 

If  the  \\ang  is  touched  with  the  fingers  dust  comes  off.  A  bit  of  the 
wing  examined  under  the  compound  microscope  shows  this  dust  to  be  com- 
posed of  tiny  scales,  which  cover  the  membranous  wing  somewhat  as  shingles 
cover  a  roof.  The  scales  give  color  to  the  wing.  Each  scale  is  fastened  in 
place  by  means  of  a  tiny  projection  which  fits  into  a  socket  of  the  wing. 
Make  a  drawing  to  show  several  scales  and  their  method  of  attachment. 

In  the  fall  the  following  questions  may  be  answered  from  living  butter- 
flies :  How  are  the  wings  used  in  flight  ?  How  are  they  held  when  at  rest  ? 
What  is  the  position  of  the  legs  when  at  rest  ?  How  are  they  used  in  walk- 
ing?    Are  any  structures  present  which  aid  in  clinging  to  objects? 

Let  the  butterfly  feed  on  sugar  and  water.  The  long  structure  which 
looks  somewhat  like  a  tiny  watch  spring  is  the  proboscis.  Compare  its  posi- 
tion when  in  use  and  not  in  use.  This  organ  is  formed  of  the  two  maxillse, 
each  of  which  forms  half  of  the  tube  through  which  the  fluid  food  is  taken 
into  the  mouth. 

The  fluffy  structures  on  each  side  of  the  mouth  are  the  labial  palps.  They 
have  to  do  with  sensation,  probably  that  of  detection  of  odors.      As  pollen 


*  It  is  not  expected  that  a  pupil  can  make  all  the  observations  noted  below 
on  the  butterfly  and  moth  as  well  as  on  their  development.  Much  of  this  work 
can  be  done  as  extra  observational  work  when  the  forms  are  obtainable.'  Work 
in  the  early  spring  (when  this  study  is  usually  taken  up)  would  preclude  the  pos- 
sibility of  some  of  the  laboratory  suggestions  outlined.  For  laboratory  directions 
see  Hunter  and  Valentine,  Manual,  page  105. 


INSECTS 


233 


carriers  they  are  of  im- 
portance. Notice  the 
large  compound  eyes  at 
the  side  of  the  head,  as  in 
the  grasshopper.  The 
antennae,  sensory  organs 
which  have  to  do  with 
hearing  and  smelhng,  are 
knobbed  at  the  ends.  The 
hairs  which  cover  the 
body  are  modified  on  the 
wings  to  form  scales. 
Some  of  these  hairs  have 
to  do  with  the  sense  of 
touch. 

The  Senses.  —  Experi- 
ments may  easily  be  made 
outdoors  in  the  fall  of  the 
year  to  determine  if  the 
butterfly  can  distinguish 
color.  Make  careful  note 
of  the  different  flowers 
visited  by  a  butterfly  dur- 
ing a  given  period  of  time. 
Are  flowers  of  certain 
colors  visited  during  that 
time  ?  Experiments  may 
also  be  made  to  see  if  the 
odors  of  flowers  are  fac- 
tors which  determine  the 
insects'  visits.  In  most 
insects  the  sense  of  smell 
is  better  developed  than 
that  of  sight.      In  most 


Monarch  butterfly;  adults,  larva,  and  pupa  on  milkweed. 
From  photograph  loaned  by  the  American  Museum  of 
Natural  History. 


butterflies  the  antennae  contain  the  sense  cells  which  have  to  do  with  odor; 
in  some  male  butterflies,  however,  a  pouch  on  the  wing  serves  as  a  help 
in  distinguishing  the  presence  of  nectar  in  a  flower. 

Make  a  drawing  of  the  butterfly,  showing  as  many  as  possible  of  the 
structures  mentioned.     Carefully  label  each  part.     A  drawing  of  the   head 

as  seen  from  the  side,   enlarged  about  four 

times,  will  be  useful. 

The  monarch  or  milkweed  butterfly 
(Anosia  plexippus)  is  one  of  our  com- 
monest insects.  Its  orange-brown,  black- 
veined  wings  are  familiar  to  every  boy  or 
girl  who  has  been  outdoors  in  the  coun- 
tiy  during  the  fall  months.  The  adult 
female  lays  her  eggs  in  the  late  spring 
on  the  milkweed.  The  eggs  are  fastened 
singly  to  the   under  side  of   milkweed 


Part  of  the  wing  of  a  moth  (Samia), 
magnified  to  show  the  arrange- 
ment of  scales. 


234  ZOOLOGY 

leaves;  they  are  tiny  sugarloaf-shaped  dots  a  twentieth  of  an 
inch  in  length.  Some  wonderful  instinct  leads  the  animal  to 
deposit  the  eggs  on  the  milkweed,  for  the  young  feed  upon  no 
other  plant.  Eggs  laid  in  May  hatch  out  in  four  or  five  days 
into  rapid-growing  caterpillars,  each  of  which  will  molt  several 
times  before  it  becomes  full  size.  The  animal  at  this  stage  is 
known  as  a  larva} 

The  Caterpillar.  —  Field  Work.  The  monarch  caterpillar  has  its  body 
covered  in  a  banded  combination  of  yellow  and  green.  Note  the  horns  that 
are  sometimes  protruded  from  the  head.  Notice  where  you  find  the  ani- 
mals; is  their  color  a  protection?  The  caterpillar  is  very  unpleasant  to 
the  taste;  by  means  of  its  conspicuous  color  the  animal  warns  birds  that 
it  is  not  good  to  eat.     This  is  known  as  warning  coloration. 

The  body  of  the  caterpillar  is  segmented  and  provided  with  several  pairs 
of  legs.  Notice  that  the  number  of  segments  is  the  same  as  in  the  adult 
butterfly.  The  true  or  butterfly  legs  are  found  on  the  anterior  segments  of 
the  body.  Compare  them  with  the  false  legs  or  prolegs  found  more  pos- 
teriorly. Notice  the  tips  of  the  legs.  How  are  the  legs  adapted  to  cling- 
ing? How  are  the  true  legs  used  when  the  caterpillar  is  feeding?  Watch 
the  caterpillar  when  it  is  feeding;  the  mouth  parts  are  very  different  from 
the  adult.  It  is  at  this  stage  that  caterpillars  are  of  considerable  economic 
importance  because  of  the  damage  they  do  to  trees  and  other  green  plants. 

Formation  of  Pupa.  —  After  a  life  of  a  few  weeks  at  most,  the 
caterpillar  stops  eating  and  begins  to  spin  a  tiny  mat  of  silk  upon 
a  leaf  or  stem.  It  attaches  itself  to  this  web  by  the  posterior 
pair  of  prolegs,  and  there  hangs  until  a  last  molt  (which  occurs 
within  twenty-four  hours  after  attachment)  gives  the  animal  the 
form  it  assumes  in  the  stage  known  as  the  chrysalis  or  pupa. 

The  Pupa.  —  Field  work.  The  chrysalis  of  the  monarch  is  green  in  color 
with  gold  spots.  It  may  be  found  upon  almost  any  green  plant,  fence,  or 
even  stone,  as  the  animal  leaves  its  food  plant  before  going  into  this  stage. 
If  you  find  one,  examine  it  carefully.  Make  out  the  three  parts  of  the  body; 
the  wings,  antennae,  and  legs  may  be  seen  closely  folded  against  the  body. 
The  spiracles  also  show  plainly. 

The  Adult.  —  After  a  week  or  more  of  inactivity  the  exoskeleton 
is  split  along  the  dorsal  side,  and  the  adult  butterfly  emerges.  At 
first  the  wings  are  soft  and  much  smaller  than  in  the  adult.  Within 
fifteen  minutes  to  half  an  hour  after  the  butterfly  emerges,  how- 
ever, the  wings  are  full  sized,  having  been  pumped  full  of  blood. 

In  the  adult  form  the  animal  may  survive  the  winter.  The 
milkweed  butterfly  is  a  strong  flyer,  and  has  been  found  over  five 

*  For  laboratory  work  see  Hu^te^  and  Valentine,  Manual,  page  107. 


INSECTS 


235 


The  monarch  and  viceroy  butterflies;  the  latter  (at  the 
right)  is  a  mimic. 


hundred  miles  at  sea. 
They  may  migrate 
southward  upon  th€ 
approach  of  the  cold 
weather.  Some  com- 
mon forms,  as  the 
mourning  cloak  (Va- 
nessa antiopa),  hiber- 
nate in  the  North, 
passing  the  cold 
weather  under  stones  or  overhanging  clods  of  earth. 

Mimicry.  —  The  monarch  butterfly  is  an  example  of  a  race  which 
has  received  protection  from  enemies  in  the  struggle  for  life, 
because  of  its  nauseous  taste  and,  perhaps,  because  its  caterpillar 
feeds  on  plants  of  no  commercial  value. 

Another  butterfly,  less  favored  by  nature,  resembles  the  monarch 
in  outward  appearance.  This  is  the  viceroy  (Basilarchia  archip- 
pus).  It  seems  probable  that  in  the  early  history^  of  the  species 
called  viceroy  some  of  this  edible  form  escaped  from  the 
birds  because  they  resembled  in  color  and  form  the  species  of 
inedible  monarchs.  These  favored  individuals  produced  new 
butterflies  which  resembled  the  monarch  more  closely.  So  for 
generation  after  generation  the  ojies  which  were  most  like  the 
inedible  species  were  left,  the  others  becoming  the  food  of  birds. 
Ultimately  a  species  of  butterflies  was  formed  that  owed  its 
existence  to  the  fact  that  it  resembled  another  more  favored  species. 
This  is  known  as  mimicry,  and  the  viceroy  is  called  a  mimic. 

Dimorphism  and  Polymorphism.  — 
It  has  been  found  that,  when  a  but- 
terfly produces  two  broods  during 
one  season,  the  individuals  in  these 
broods  may  differ  considerably  from 
one  another.  The  tiger  swaliow-tail 
is  an  example.  It  has  also  been 
found  that,  if  the  early  pupae  are 
kept  in  an  ice  box  during  part 
of  the  summer  and  then  allowed 
to  hatch  out  with  the  pupae  of 
the  second  brood,  the  forms  are 
then  ahke  in  appearance.  It  would 
Hornet  mimicked  by  locust-borer,  a  beetle.       thus  seem    that    the    same    factors 


2S6 


ZOOLOGY 


which  play  such  important  parts  ii? 
the  life  of  plants  also  play,  in  some 
cases  at  least,  equall}''  important  parts 
in  molding  the  form  and  structure  of 
animals. 

The  Moth.  —  The  Cecropia  (Samia 
cecropia)  may  be  used  for  laboratory 
work.  Note  the  general  resemblance 
to  the  butterfly.  Several  differences 
may  be  noticed,  however.  The  body 
is  much  stouter  than  that  of  the 
butterfly.  The  wings  and  body  ap- 
pear to  have  a  thicker  coating  of 
hairs  and  scales.  Notice  also  the 
feathery  antennae.  What  is  the  rest- 
ing position  of  the  wings?  When  you 
draw  the  moth,  be  sure  to  show  the 
color  markings  of  the  wings. 

The  Egg.  —  The  eggs,  cream- 
colored  and  as  large  as  a  pin 
head,  are  deposited  in  small 
clusters  on  the  under  side  of 
leaves  of  the  food  plant.  The 
young  are  at  first  tiny  black 
caterpillars,  which  later  change 
color  to  a  bluish  green,  with 
projections  of  blue,  yellow,   and   red   along   the   dorsal   side. 

Study  of  Caterpillar.  —  Captive  Cecropias  will  frequently  lay  eggs  which 
may  be  watched  in  development  by  placing  the  young  caterpillars  in  a  box 
with  leaves  of  willow  or  wild  cherry.  Watch  such  an  animal,  and  describe 
the  process  of  molting.  Which  end  molts  first?  How  do  they  get  out  of 
the  old  skin  ?  Is  the  color  of  the  feeding  caterpillars  like  that  of  the  leaves  ? 
On  which  side  of  the  leaves  do  they  rest  ?  How  are  the  leaves  held  in  feed- 
ing?    Are  any  other  parts  of  the  animal  besides  the  jaws  used  in  feeding? 

The  Pupal  Stage.  —  Unlike  the  butterfly,  the  moth  passes  the 
quiescent  stage  in  a  case  of  silk  or  other  material  called  a  cocoon. 
The  cocoons  of  Cecropia  may  be  found  in  the  fall  on  willows  or 
alders.  Such  cocoons  found  in  meadows  or  fields  are  usually 
larger  than  those  found  on  the  hillsides,  probably  because  of  a 
difference  in  the  food  supply  of  the  larva  which  spun  the  cocoon. 

Study  of  a  Cocoon  and  Pupa}  —  Where  do  you  find  them,  and  how  are 
they  attached?  Of  what  materials  is  the  cocoon  made?  An  interesting 
report  would  be  the  formation  of  the  cocoon.     This  may  be  watched  by 


The  tiger  swallow-tail,  showing  two  forms 
of  females. 


*  See  Hunter  and  Valentine,  Manual,  page  108. 


INSECTS 


237 


cutting  off  the  food  sup- 
ply of  caterpillars  in  cap- 
tivity as  they  will  usually, 
in  such  event,  at  once 
begin  the  spinning  of  a 
cocoon. 

If  the  cocoon  is  cut 
open  lengthwise,  the  dor- 
mant insect  or  chrj'salis 
will  be  found  together 
with  the  cast-off  skin  of 
the  caterpillar  which  spun 
the  case.  You  can  easily 
make  out  the  parts  of  the 
adult  moth,  the  antennae 
and  wings  folded  close  to 
the  body.  Notice  how 
the  head  and  thorax  are 
crowded  together.  Find 
the  weak  spot  in  the 
cocoon  through  which  the 
adult  makes  its  escape. 
Draw  the  pupa  in  the 
cocoon,  and  label  all  its 
parts. 

Silkworms.  —  The 
American  silkworm 
(Telea  polyphemus)  is 
another      well-known 


Life  history  of  the  Cecropia  moth.    Above,  the  adult;  the 
larva  (caterpillar)  in  center;   the  pupal  case  to  right, 
below;  the  same  cut  open  at  left,  below.    From  photo- 
graph loaned  by  the  American  Museum  of  Natural 
History. 


moth.  The  cocoons, 
made  in  part  out  of  the  leaves  of  the  elm,  oak,  or  maple,  fall  to 
the  ground  when  the  leaves  drop,  and  hence  are  not  so  easily 
found  as  those  of  the  Cecropia.  This  moth  is  a  near  relative 
of  the  Chinese  silkworm,  and  its  silk  might  be  used  with  success 

were  it  not  for  the  high 
rate  of  labor  in  this  coun- 
try. The  Chinese  silk- 
worm is  now  raised  with 
ease  in  southern  California, 
China,  Japan,  Italy,  and 
France,  because  of  cheap 
labor,  are  still  the  most 
successful  silk-raising 
_  ,  ^  ,  ,.     ^     ,  .       „.  ,        ,    .     countries.    It  is  estimated 

Folyphemus,  one  half  natural  size.    Jrhotograpneu 

by  Davison.  that  it  takes  the  silk  from 


238 


ZOOLOGY 


at  least  twenty-five  thousand  cocoons  to  form  the  material  for 
a  single  dress. 

Harm  done  by  Moth  Larvag.  —  From  the  economic  standpoint 
the  harm  done  by  the  moths  far  outweighs  the  good  they  may 

have  done.  Although  they  pol- 
linate flowers  to  some  extent, 
still  the  butterflies  are  greater 
bearers  of  pollen.  Great  dam- 
age is  done  annually  by  the 
larvae  of  moths.  Massachusetts 
has  spent  some  $3,000,000  in 
trying  to  exterminate  the  im- 
ported gypsy  moth.  The  cod- 
ling moth,  which  bores  into 
apples  and  pears,  is  estimated 
to  ruin  yearly  $3,000,000  worth 
of  fruit  in  New  York.  Among 
these  pests,  the  most  important 
to  the  dweller  in  a  large  city  is 
the  tussock  moth  which  de- 
stroys our  shade  trees.     The  caterpillar  may  easily  be  recognized 


i 

'^, 

% 

L     ' 

'^ 

s,^ 

Female  tussock  moth  which  has  just  emerged 
from  the  cocoon  at  the  left  upon  which  it 
has  deposited  over  two  hundred  eggs. 
From  photograph,  slightly  enlarged,  by 
Davison. 


Larva  of  tussock  moth.    From  photograph,  twice  natural  size,  by  Davisono 


INSECTS  239 

by  its  hairy,  tufted  red  head.  The  eggs  are  laid  on  the  bark  of 
shade  trees  in  what  look  like  masses  of  foam.  By  collecting 
and  burning  the  egg  masses  in  the  fall,  we  may  save  many  shade 
trees  the  following  year. 

Other  enemies  of  the  shade  trees  are  the  fall  webworm,  the  forest 
caterpillar,  and  the  tent  caterpillar;  the  last  spins  a  tent  which 
serves  as  a  shelter  in  wet  weather.  Among  the  greatest  enemies 
to  crops  are  the  cankerworm,  the  measuring  worm,  the  corn 
worm,  and  the  cotton-boll  worm.  The  last  annually  damages  the 
cotton  crop  to  the  amount  of  several  millions  of  dollars. 

The  larvse  of  the  peach,  apple,  and  other  fruit  borers  damage 
the  trees  by  boring  into  the  wood  of  the  tree  on  which  they  live. 
The  clothes  moth,  a  well-known  house  pest,  lays  its  eggs  in  woolen 
materials,  upon  which  the  larvae  feed. 

Differences  between  Moths  and  Butterflies 

Butterfly  Moth 

Antennae     threadlike,  usually     Antennae      feathery     or    rarely 

knobbed  at  tip.  threadlike,    never   knobbed. 

Fly  in  daytime.  Usually  fly  at  night. 

Wings  held  vertically  when  at     Wings     held     horizontally     or 

rest.  folded  over   the   body  when 

at  rest. 

Pupa  naked.  Pupa  covered  by  a  cocoon. 

Adaptations.  —  Butterflies  and  moths  are  wonderfully  adapted 
to  the  lives  they  lead.  Instinct  leads  them  to  place  the  eggs  on 
the  food  plant  where  food  is  provided  for  the  young.  The  edible 
larvae  are  often  colored  like  the  plants  on  which  they  rest,  those 
not  good  to  eat  receive  immunity  by  having  bright  colors  or  con- 
spicuous markings  which  warn  away  their  enemies. 

The  protective  coloration  which  has  been  developed  in  some 
species  of  butterflies  undoubtedly  plays  an  important  part  in 
preserving  those  species.  One  of  the  most  interesting  examples  of 
this  is  seen  in  the  case  of  the  dead-leaf  butterfly  of  India. ^  This 
butterfly  at  rest  exactly  resembles  a  dead  leaf;  in  flight  it  is  con- 


240 


zoClogy 


spicuous.  The  underwing  moth  is 
another  example  of  a  wonderful  sim- 
ulation of  the  background  of  bark 
on  which  the  animal  rests  in  the 
daytime.  At  night  the  brightly  col- 
ored under  wings  probably  give  a 
signal  to  others  of  the  same  species. 
The  beautiful  luna  moth,  in  color  a 
delicate  green,  rests  by  day  among 
the  leaves  of  the  hickor}^  The  small 
measuring  worms  stand  out  stiff  upon 
the  branches  on  which  they  crawl, 
thus  simulating  lateral  twigs.  Hun- 
dreds of  other  examples  might  be 
given. 

This  likeness  of  an  animal  to  its 
immediate  surroundings  has  already 
been  noted  as  ^protective  resemblance. 

Reference  Books 

The  underwing  moth;  above,  flying;  p^j^  ^jj^,   PUPIL, 

below,  at  rest  on  bark. 

Burnet,  »Sc/20oZ  ZooZogr?/,  pages  101-111.  American  Book  Company. 

Davison,  Practical  Zoology,  pages  68-91.     American  Book  Company. 

Herrick,  Text-book  in  General  Zoology,  Chap.  XV.     American  Book  Company. 


FOR   THE    TEACHER 

Dodge,  General  Zoology,  pages  113-118.     American  Book  Company. 

Dickerson,  Moths  and  Butterflies.     Ginn  and  Company. 

Sanderson,  Insects  Injurious  to  Staple  Crops.     John  Wiley  and  Sons. 

The   J'lies 

The  House  Fly}  —  Examine  a  house  fly,  find  the  divisions  of  the  body. 
Notice  the  small  hairs  covering  parts  of  it.  The  wings  appear  to  be  only 
two  in  number  —  hence  the  name  Diptera.  Behind  the  gauzy  wings  you 
will  find  the  second  pair  of  wings  have  developed  as  knobbed  hairs,  called 
the  balancers.  They  seem  to  have  the  double  function  of  giving  aid  in 
balancing  and  in  hearing. 

Notice  the  shape  of  the  head.  Is  it  freely  movable?  The  antennae  are 
very  short,  while  the  eyes  are  enormously  developed.     Test  with  moving 

*  See  Hunter  and  Valentine,  Mamud,  page  114. 


INSECTS 


241 


objects  the  keenness  of  vision  and  especially  the  distance  at  which  a  flj 
notices  movement  of  an  object. 

Feed  the  fly  with  a  drop  of  sugar  solution.  Study  the  movement  of  the 
organ  called  the  proboscis.  This  proboscis  is  made  up  chiefly  of  the  maxillsE, 
together  with  the  labial  palps,  the  mandible  being  undeveloped.  P'ood  is 
obtained  by  lapping  and  sucking.  Notice  the  flaplike  extensions  on  each 
side  of  the  proboscis;  these  are  roughened  on  the  under  surface.  It  is  the 
rubbing  of  this  filelike  organ  over  the  surface  of  the  skin  that  causes  the 
painful  bite  of  the  horse  fly.  If  possible,  examine  the  foot  of  a  fly  under  a 
low  magnification  of  the  compound  microscope.  The  foot  shows  a  won- 
derful adaptation  for  clinging  to  smooth  surfaces.  Two  or  three  pads,  each 
of  which  bears  tubelike  hairs  that  secrete  a  sticky  fluid,  are  found  on  its 
under  surface.     It  is  by  this  means  that  the  fly  is  able  to  walk  upside  down. 

Home  Experiments. — Test  the  keenness  of  scent  in  the  fly  by  placing  in 
an  exposed  place  a  bit  of  meat,  some  bread,  salt,  sugar,  and  other  foods, 
some  of  which  have  distinct  odor.  Cover  each  food  with  tissue  paper. 
Which  food  attracts  the  most  flies  ? 

Test  the  sense  of  taste  of  the  fly  by  the  following  experiment. 

Place  in  a  netting  cage  four  butter  chips  containing  a  solution  of  sugar, 
salt,  alum,  and  strychnine  or  other  bitter  fluid.  Place  in  the  cage  a  number 
of  flies,  and  at  the  end  of  a  given  period  count  the  number  at  each  dish.  Do 
flies  appear  to  have  the  sense  of  taste  ? 


Life  history  of  house  flies,  showing  from  left  to  right  the  eggs,  larvao,  pupae,  and  adult  flies. 

Photograph,  about  natural  size,  by  Overton. 

The  House  Fly  a  Pest.  —  The  house  fly  is  recognized  the  world 
over  as  a  pest.  Not  only  do  flies  spoil  much  food  by  means  of 
their  filthy  habits,  but  the  far  more  important  charge  of  spreading 
disease  is  now  laid  to  them.  The  bacteria  causing  typhoid  fever 
might  be  carried  on  their  feet;  so  flies  could  easily  carry  the 
typhoid  bacteria  to  a  dish  of  milk,  thus  infecting  the  milk  and 
causing  danger  to  all  drinking  it. 

Development.  —  The  development  of  the  house  fly  is  very  rapid. 

hunter's    BIOL.  —  16^ 


242  ZOOLOGY 

A  female  may  lay  from  one  hundred  to  two  hundred  eggs.  These 
are  usually  deposited  in  filth  or  manure.  In  warm  weather  within 
a  da}'  after  the  eggs  are  laid  the  young  maggots,  as  the  larvse  are 
called,  hatch.  After  about  one  week  of  active  feeding  these  worm- 
like maggots  become  quiet  and  go  into  the  pupal  stage,  whence 
under  favorable  conditions  they  emerge  within  another  week  as 
adult  flies.  The  adults  breed  at  once,  and  in  a  short  summer 
there  may  be  over  ten  generations  of  flies.  This  accounts  for  the 
great  number.     Fortunately  few  flies  survive  the  winter. 

The   Mosquito.  —  Among   the   flies   are   some   of   the   greatest 
human  pests.     The  mosquito  is  one  relative  which  is  known  to 


Three  pupse  and  two  larvae  of  mosquitoes  at  the  surface  of  the  water,  breathing.     The  black 
line  is  the  water  surface.    From  photograph  from  life,  twice  natural  size,  by  Davison. 

harbor  the  small  one-celled  parasite  (a  protozoan)  which  causes 
malaria.  Another  species  of  mosquito  is  a  carrier  of  yellow  fever. 
Mosquitoes  lay  eggs  in  tiny  rafts  of  one  hundred  or  more  eggs  in 
any  standing  water.  Rain  barrels,  gutters,  or  old  cans  may  breed 
in  a  short  time  enough  mosquitoes  to  stock  a  neighborhood.  The 
larvae  are  known  as  wigglers.  They  breathe  through  a  tube  in  the 
posterior  end  of  the  body  and  may  be  recognized  by  their  peculiar 
movement  when  on  their  way  to  the  surface  to  breathe.  The  fact 
that  both  larvae  and  pupae  take  air  from  the  surface  of  the  water 
makes  it  possible  to  kill  the  mosquito  during  these  stages  by  pour- 
ing crude  oil  on  the  surface  of  the  water  where  they  breed.  The 
introduction  of  goldfish  or  other  small  fish  into  water  where  they 
breed  is  another  effective  means  of  kilUng  this  pest. 

Economic  Importance  of  Other  Flies.  —  Other  flies  which  are  of 


INSECTS 


243 


great  economic  importance  are  the  Hessian  fly,  the  larvae  of  which 
feeds  on  young  wheat;  the  bot  fly,  which  in  a  larval  state  is  a 
parasite  on  horses;  the  dreaded  tsetse  fly  of  South  Africa,  which 
is  now  believed  to  cause  disease  in  horses  and  cattle  by  means  of 
the  transference  of  a  parasitic  protozoan,  much  like  that  which 
causes  malaria  in  man;  and  many  others. 

Among  the  few  flies  useful  to  man  may  be  mentioned  the 
fcachina  flies,  the  larvae  of  which  feed  on  the  cut  worm,  the  army 
worm,  and  various  other  kinds  of  injurious  caterpillars. 

Reference  Books 

for  the  pupil 

Davison,  Practical  Zoology,  pages  39-52.     American  Book  Company. 
Herrick,  Text-hook  in  General  Zoology,  pages  183-186.     American  Book  Company. 
Farmers*  Bulletin.     How  Insects  affect  Health  in  Rural  Districts.     U.S.  Department 
of  Agriculture. 

The  Order  Neuroptera 


The  Dragon  Fly. — The  dragon  fly  receives  its  name  because  it  preys  on 
insects.  It  eats,  when  an  adult,  mosquitoes  and  other  insects  which  it  cap- 
tures while  on  the  wing.  Its  large 
lacelike  wings  give  it  power  of  very 
rapid  flight,  while  its  long  narrow 
body  is  admirably  adapted  for  the 
same  purpose.  The  large  com- 
pound eyes  placed  at  the  sides  of 
the  head  give  keen  sight.  Notice 
the  powerful  jaws  (almost  covered 
by  the  upper  and  lower  lips). 
Compare  the  position  of  the  wings 
when  at  rest  with  those  of  the 
grasshopper.  The  wings  in  this 
case  are  adapted  for  swift  flight. 

The  long  thin  abdomen  does  not 
contain  a  sting,  contrary  to  the  be- 
lief of  most  children.  These  in- 
sects deposit  their  eggs  in  the  water,  and  the  fact  that  they  may  bo  often 
seen  with  the  end  of  the  abdomen  curved  down  under  the  surface  of  the 
water  in  the  act  of  depositing  the  eggs,  has  given  rise  to  the  behcf  that 
they  were  then  engaged  in  stinging  something.  The  egg  hatches  into  a 
form  of  larva  called  a  nymph,  which  in  the  dragon  fly  is  characterized 
by  a  greatly    developed  lower  lip.       When   the   animal  is  at   rest,  the 


Dragon  fly. 


Notice  the  long  abdomen  and  large 
compound  eyes. 


244  ZOOLOGY 

lower  lip  covers  the  large  biting  Jaws  which  can  be  extended  so  as  to 
grasp  and  hold  its  prey.  The  nymphs  of  the  dragon  fly  take  oxygen  out 
of  the  water  by  means  of  gill-like  structures  placed  in  the  posterior  part  of 
the  food  tube.  They  may  live  as  larvae  from  one  summer  to  as  long  as  two 
years  in  the  water.  Thej'  then  crawl  out  on  a  stick,  molt  by  splitting  the 
skin  down  the  back,  and  come  out  as  adults. 

A  nearly  related  form  is  the  damsel  fly.  This  may  be  distinguished  from 
the  dragon  fly  by  the  fact  that  when  at  rest  the  wings  are  carried  close  to 
the  abdomen,  while  in  the  dragon  fly  they  are  held  in  a  horizontal  position.^ 

May  Flies. — Another  near  relative  of  the  dragon  fly  is  the  May  fly. 
These  insects  in  the  adult  stage  have  lost  the  power  to  take  food.  Most 
of  their  life  is  passed  in  the  larval  stage  in  the  water.  The  adults  some- 
times live  only  a  few  hours,  just  long  enough  to  deposit  their  eggs. 

The   Order   Coleoptera 

Beetles.  —  Beetles  are  the  most  widely  distributed  of  all  insects 
and  by  far  the  most  numerous.  There  are  over  one  hundred  thou- 
sand living  species;  more  than  all  other  animals  in  the  world 
exclusive  of  the  insects. 

Any  beetle  will  show  the  following  characteristics:^  (1)  The 
body  is  usually  heavy  and  broad.  Its  exoskeleton  is  hard  and 
tough.  The  lower  side  of  the  abdomen  is  also  hard.  The  chitinous 
covering  is  better  developed  in  the  beetles  than  in  any  other  of  the 
insects.  (2)  The  three  pairs  of  legs  are  stout  and  rather  short. 
(3)  The  outer  wings  are  hard  and  fit  over  the  under  wings  like  a 
shield.  These  sheathlike  wings  are  called  elytra.  (4)  The  mouth 
parts  are  fitted  for  biting.  They  consist  of  very  heavy  curv^ed 
pincher-shaped  mandibles,  which  are  provided  with  palps.  There 
is  an  upper  and  lower  lip. 

The  Living  Beetle.  —  Use  any  large  beetle  to  answer  the  following  questions. 
Identify  the  above-named  parts  in  3'^our  specimen.  Test  the  ability  of 
any  large  beetle  to  bite.  Are  the  jaws  strong?  Give  proofs.  Do  the  jaws 
move  in  the  same  plane  with  your  own?  Does  the  beetle  have  antennae 
(feelers)  ?  How  does  the  beetle  use  its  legs  in  walking  ?  Is  there  any 
regular  order?  If  the  animal  is  allowed  to  walk  over  an  ink  pad  or  through 
a  drop  of  ink,  its  track  may  easily  be  traced  on  paper  and  then  transferred 
to  your  notebook.  In  what  respects  is  the  beetle  protected  from  its 
enemies  ?     How  is  it  adapted  to  the  life  it  leads  ? 

^  The  old  seven-order  system  of  classification  is  useful  for  pupils  of  first  year  in 
the  high  school.  Tliis  allows  a  place  for  many  forms  otherwise  not  easily  classified 
under  the  order  Neuro-ptera. 

2  For  laboratory  directions  on  beetles,  see  Hunter  and  Valentine,  Maniuil,  page 


INSECTS 


245 


Make  a  drawing  of  the  beetle,  natural  size,  to  show  as  many  of  the  above 

parts  as  possible. 

The  Life  History  of  a  Beetle.  —The  June  bug  (May  beetle)  and 
potato  beetle  are  excellent  examples.  May  beetles  lay  their  eggs  in 
the  ground,  where  they  hatch  into  cream-colored  grubs.  A  grub 
differs  from  the  larval  fly  or  maggot  in  possessing  three  pairs  of 
legs.  These  grubs  live  in  burrows  in  the  ground.  Here  they  feed 
on  the  roots  of  grass  and  garden  plants.  The  larval  form  remains 
underground  for  from  two  to  three  years,  the  latter  part  of  this 
time  as  an  inactive  pupa.  During  the  latter  stage  it  lies  dormant 
in  an  ovoid  area  excavated  by  it.  Eventually  the  wings  (which 
are  budlike  in  the  pupa)  grow  larger,  and  the  adult  beetle  emerges 
fitted  for  its  life  in  the  open  air. 

Economic  Importance.  — ■  Among  the  beetles  which  are  of 
economic  importance  is  the  potato  beetle  which  destroys  the  po- 
tato plant.  This  beetle 
formerly  lived  in  Colo- 
rado upon  a  wild  plant 
of  the  same  family  as 
the  potato  and  came 
east  upon  the  introduc- 
tion of  the  potato  into 
Colorado,  evidently  pre- 
ferring cultivated  forms 
to  wild  forms  of  this 
family.  The  snout 
beetles  or  weevils  do 
much  damage  to  stored 
grains  and  fruits.  Other 
beetles  known  as  the 
borers  produce  larvae 
which  bore  into  trees 
and  then  feed  upon  the  sap  of  the  tree.  Many  trees  in  our  Adiron- 
dack Forest  Reserve  annually  succumb  to  these  pests.  Most  fallen 
logs  will  repay  a  search  for  the  larvae  which  bore  between  the  bark 
and  wood.  Among  the  most  destructive  of  all  in  city  homes  are 
the  carpet  beetles. 


Cotton-boll  weevil;  o,  larva;  b.  pupa;  c,  adult.     From 
photograph,  enlaiged  four  times,  by  Davison, 


246 


ZOOLOGY 


Firefly.  —  One  form  not  usually  considered  by  boys  and  girls 
as  a  beetle  is  the  firefly.  The  light  produced  by  this  beetle  is 
believed  by  scientists  to  be  caused  by  a  true  oxidation  of  fatty 
substances  stored  in  the  cells  of  the  lower  surface  of  the  abdomen. 
Beetles  Useful  to  Man.  —  Several  beetles  are  of  value  to  man. 
Most  important  of  these  is  the  natural  enemy  of  the  orange-tree 

scale,  the  ladybug,  or  ladybird  beetle.  This 
insect  preys  upon  the  scale  insect.  In  New 
York  state  it  may  often  be  found  feeding 
upon  plant  lice  or  aphids  which  live  on  rose 
bushes.  The  carrion  beetles  and  many„water 
beetles  act  as  scavengers.  The  sexton  beetles 
bury  dead  carcasses  of  animals.  These  beetles 
are  provided  with  antennae  that  have  the  end 
segments  peculiarly  modified  for  the  purpose 
of  smelling. 

Sexual  Dimorphism.  —  Among  beetles,  as  among 
other  insects,  the  two  sexes  sometimes  show  marked 
differences.  This  is  particularly  well  shown  in  the 
case  of  the  stag  beetle,  shown  in  the  illustration. 
This  difference  in  form  between  male  and  female  of 
a  given  species  is  known  as  sexual  dimorphism. 

Hemiptera 

Bugs.  —  The  cicada,  or  as  it  is  incorrectly 
called,  the  locust,  is  a  familiar  insect  to  all. 
Its  droning  song  is  one  of  the  accompani- 
ments of  a  hot  day.  The  song  of  the  cicada 
is  produced  by  a  drumlike  organ  which 
can   be  found  just  behind  the   last   pair  of 

legs.     The  sound  is  caused  by  a  rapid  vibration  of  the  tightly 

stretched  drumhead. 

Characteristics  of  the  Cicada. — In  a  living  animal  notice  that  the  body 
is  heavy  and  bulky.  The  wings,  four  in  number,  are  relatively  small,  but 
the  powerful  muscles  give  them  very  rapid  movement.  The  anterior  wings 
are  larger  than  the  posterior.  The  legs  are  not  large  or  strong ;  the  move- 
ment when  crawling  being  sluggish.  Note  the  color  of  the  body;  evidently 
the  insect  depends  upon  protection  by  means  of  assuming  the  colors  of  the 


The  stag  beetle,  showing 
sexual  dimorphism. 
Male  above,  female 
below.    Natural  size. 


INSECTS 


247 


objects  on  which  it  rests.  The  principal  characteristics  of  the  cicada,  and 
of  all  bugs,  is  that  the  mouth  parts  are  prolonged  into  a  beak  with  which 
the  animal  first  makes  a  hole  and  then  sucks  up  the  juices  of  the  plants  on 
which  it  lives. 

Life  History.  —  The  17-year  cicada  lays  her  eggs  in  twigs  of  trees 
and  in  doing  this  causes  the  death  of  the  twig.  The  young  leave 
the  tree  immediately  after  hatching,  burrow  under  ground,  and 
pass  from  thirteen  to  seventeen  years  there.  In  the  South  this 
period  is  shortened.  They  live  by  sucking  the  juices  from  roots. 
During  this  stage  they  somewhat  resemble  the  grub  of  the  beetle 
(June  bug)  in"  habits  and  appearance.      When  they  are  about  to 


s 


Cicada:  1,  adult  with  wings  spread,  showing  abdomen  {Ah.),  head  (//.),  thorax  {Th.); 
S,  pupal  case,  showing  the  split  down  the  back;  3,  ventral  view,  showing  beak  (fi.),  eye,  {£.). 

molt  into  an  adult,  they  climb  above  ground,  cling  to  the  bark  of 
trees,  and  then  crawl  out  of  the  skin  as  adults. 

Economic  Importance.  —  The  bugs  are  among  our  most  de- 
structive insects.  The  most  familiar  examples  of  our  garden  pests 
are  the  squash  bug;  the  chinch  bug,  which  yearly  does  damage 
estimated  at  $20,000,000  by  sucking  the  juice  from  the  leaves  of 
grain;  the  scale  insects,  our  greatest  fruit  tree  pests,  especially  in 
the  orange  groves  of  California;   and  the  plant  lice  or  a])hids. 

Aphids.  —  The  aphids  are  among  the  most  interesting  of  the  he- 
miptera.  They  are  familiar  to  all  as  the  tiny  green  lice  seen  swarm- 
ing on  the  stems  and  leaves  of  the  rose  and  other  cultivated  plants. 


248 


ZOOLOGY 


They  suck  the  juices  from  stem  and  leaf.  Plant 
lice  have  a  remarkable  life  history.  Early  in 
the  year  eggs  develop,  into  wingless  females, 
which  produce  living  young,  all  females.  These 
in  turn  reproduce  in  a  similar  manner,  until 
the  plant  on  which  the}'  live  becomes  over- 
crowded and  the  food  supply  runs  short.  Then 
a  generation  of  winged  aphids  is  produced. 
These  fly  away  to  other  plants,  and  reproduc- 
tion goes  on  as  before  until  the  approach  of 
cold  weather,  when  males  and  females  appear. 
Fertilized  eggs  are  then  produced  which  give 
rise  to  young  the  following  season. 

The   aphids   exude  from  the  surface   of   the 
body  a  sweet  fluid  called   honeydew.     This  is 
given  off  in  such  abundance  that  it  is  estimated 
Maple  scale,  tive  adults    if  au  aphid  Were  the  size  of  a  cow  it  would 
iVom°'photorr^h     S'^^^  ^^^  thousaud  quarts  a  day.     This  honey- 
eniarged  twice,  by    dew  is  greatly  esteemed  by  other  insects,  es- 
pecially the  ants.     For  the  purpose  of  obtaining 
it,  some  ants  care  for  the  aphids,  even  providing  food  and  shelter 
for  them.     In  return  the  aphid,  stimulated  by  a  stroking  move- 
ment of  the  antenna  of  the  ant,  gives  up  the  honeydew  to  its 
protector. 

Some  aphids  are  extremely  destructive  to  vegetation.  One,  the 
grape  Phylloxera,  yearly  destroys  immense  numbers  of  vines  in 
the  vineyards  of  France,  Germany,  and  California. 


The   Order   Hymenoptera 

This  order  contains  some  of  the  most  highly  developed  insects. 
We  have  already  learned  something  of  the  structure  and  habits 
of  the  bees,  in  connection  with  the  study  of  the  pollination  of 
flowers.  Let  us  now  find  out  about  their  wonderful  communal 
life.  In  the  order  Hymenoptera  are  placed  bees,  ants,  and  wasps, 
insects  which  have  developed  a  complicated  social  life.  In  connec- 
tion with  this  communal  life,  nature  has  worked  out  a  division  of 


INSECTS 


249 


labor  which  is  very 
remarkable.  This  can 
be  seen  in  tracing  out 
the  lives  of  several  of 
the  communal  insects. 

Solitary  Wasps.  — 
Some  bees  and  wasps 
lead  a  solitary  exist- 
ence. The  solitary 
and  digger  wasps  do 
not  live  in  communi- 
ties. Each  female  con- 
structs a  burrow  in 
which  she  lays  eggs 
and  rears  her  young. 
The  young  are  fed 
upon  spiders  and  in- 
sects previously 
caught  and  then  stung 
into  insensibility.  The 
nest  is  closed  up  after 
food  is  supplied  and 
the  young  later  gnaw 

their  way  out.     In  the  life  history  of  such  an  insect  there  is  no 
communal  life. 

Bumblebee.  —  In  the  life  history  of  the  big  bumblebee  we  see 
the  beginning  of  the  community  instinct.  Some  of  the  female 
bees  (known  as  queens)  survive  the  winter  and  lay  their  eggs  the 
following  spring  in  a  mass  of  pollen,  which  has  been  previously 
gathered  and  placed  in  a  hole  in  the  ground.  The  young  hatch  as 
larvae,  then  pupate,  and  finally  become  workers,  or  females.  In 
the  working  bee  the  egg-laying  apparatus,  or  ovipositor,  is  modi- 
fied to  be  used  as  a  sting.  The  workers  bring  in  pollen  to  the 
queen,  in  which  she  lays  more  eggs.  Several  broods  of  workers 
are  thus  hatched  during  a  summer.  In  the  early  fall  a  brood  of 
males  or  drones,  and  egg-laying  females  or  queens,  are  produced 
instead  of  workers. 


Ants  and  their  "  cows.' 


250 


ZOOLOGY 


It  is  by  means  of  these  egg-producing  females  that  the  brood  is 
started  the  following  year,  as  stated  on  the  preceding  page. 

The  Honeybee.  —  The 
most  wonderful  commu- 
nal life  is  seen,  however, 
among  the  honeybees. 
Their  daily  life  may  be 
easily  watched  in  the 
schoolroom,  by  means  of 
one  of  the  many  good 
and  cheap  observation 
hives  now  made  to  be 
placed  in  a  window 
frame. ^ 

The  honeybee  in  a 
wild  state  makes  its 
home  in  a  hollow  tree; 
hence  the  term  bee  tree. 
In  the  hive  the  colony 
usually  consists  of  a 
queen,  or  egg-laying 
female,  a  few  hundred 
drones,  or  males,  and 
several  thousand  work- 
ing females,  or  workers. 
The  colonies  vary  greatly 
in  numbers.  In  a  wild 
state  there  are  fewer  making  up  the  colony.  The  division  of  labor 
is  well  seen  in  a  hive  in  which  the  bees  have  been  living  for  some 
weeks.  The  queen  does  nothing  except  lay  eggs,  sometimes  laying 
three  thousand  eggs  a  day  and  keeping  this  up,  during  the  warm 
weather,  for  several  years.  She  may  lay  one  million  eggs  during 
her  life.     She  does  not,  as  is  popularly  believed,  rule  the  hive,  but 


Nests  of  solitary  wasps  on  an  apple  leaf.    From 
photograph  by  Overton, 


^  Directions  for  making  a  small  observation  hive  for  school  work  can  be  found 
in  Hodge,  Nature  Study  and  Life,  Chap.  XIV.  Bulletin  No.  1,  U.S.  Department 
of  Agriculture,  entitled  The  Honey  Bee,  bj^  Frank  Benton,  is  valuable  for  the  ama- 
teur bee  keeper.  It  may  be  obtained  for  twenty-five  cents  from  the  Superintendent 
of  Documents,  Union  Building,  Washington,  D.C. 


INSECTS 


251 


is,  on  the  contrary,  a  captive  most  of  her  life.  Most  of  the  eggs 
are  fertilized  by  the  sperm  cells  of  the  males;  the  unfertilized 
eggs  develop  into  males  or 
drones.  After  a  short  exist- 
ence in  the  hive  the  drones 
are  usually  driven  out  by  the 
workers.  The  fertilized  eggs 
may  develop  into  workers,  or, 
if  the  young  larva  is  fed  with 
a  certain  kind  of  food,  it  will 
develop  into  a  young  queen. 

The  cells  of  the  comb  are 
built  by  the  workers  out  of 
wax  secreted  from  the  ven- 
tral surface  of  the  bodies. 
The  wax  is  cut  off  in  thin 
plates  by  means  of  the  wax 
shears  between  the  two  last 
joints  of  the  hind  legs.  These 
cells  are  used  by  the  queen  to 
place  her  eggs  in,  one  to  each  cell,  and  the  young  are  hatched 
after  three  days  to  begin  life  as  footless  white  grubs. 


Hornets'  nest,  opened  to  show  the  cells  of  the 
comb.    From  photograph  by  Overton. 


Honeybees;  a,  drone;  h,  worker;  c,  queen.    From  photograph  by  Davison. 

For  a  few  days  they  are  fed  on  partly  digested  food  called  bee 
jelly,  regurgitated  from  the  stomach  of  the  workers.  Later  they 
receive  pollen  and  honey  to  eat.     A  little  of  this  mixture,  known 


252 


ZOOLOGY 


as  beebread,  is  then  put  into  the  cell,  the  lid  covered  with  wax 
by  the  working  bees,  and  the  young  larvae  allowed  to  pupate. 
After  about  two  weeks  of  quiescence  in  the  pupal  state,  the  adult 
worker  breaks  out  of  the  cell  and  takes  her  place  in  the  hive, 
first  caring  for  the  young  as  a  nurse,  later  making  excursions  to 
the  open  air  after  food  as  an  adult  worker. 

If  new  queens  are  to  be  produced,  several  of  the  cell  walls  are 
broken  down  by  the  workers,  making  a  large  ovoid  cell  in  which 
one  egg  develops.  The  young  bee  in  this  cell  is  fed  during  its 
whole  larval  life  upon  bee  jelly  and  grows  to  a  much  larger  size 
than  an  ordinary  worker.  When  a  young  queen  appears,  great 
excitement  pervades  the  community;  the  bees  appear  to  take 
sides;  some  remain  with  the  young  queen  in  the  hive,  while  others 
follow  the  old  queen  out  into  the  world.  Here  they  usually  settle 
around  the  queen,  often  hanging  to  the  limb  of  a  tree.  This  is 
called  swarming.  This  instinct  is  of  vital  importance  to  the  bees, 
as  it  provides  them  with  a  means  of  forming  a  new  colony.  For 
while  the  bees  are  swarming,  certain  of  the  workers,  acting  as 
scouts,  determine  on  a  site  for  their  new  home;  and,  if  un- 
disturbed, the  bees  soon  go  there  and  construct  their  new  hive. 
A  swarm  of  domesticated  bees,  however,  may  be  quickly  hived 
in  new  quarters. 

We  have  already  seen  (see  pages  37  and  38)  that  the  honeybee 
gathers  nectar  which  she  swallows,  keeping  the  fluid  in  her  crop 
until  her  return  to  the  hive.  Here  it  is  regurgitated  into  cells 
of  the  comb.  It  is  now  thinner  than  what  we  call  honey.  To 
thicken  it  the  bees  swarm  over  the  open  cells,  moving  their 
wings  very  rapidly,  thus  evaporating  some  of  the  water  in  the 
honey.     A  hive  of  bees  have  been  known  to  make  over  thirty-one 

pounds  of  honey  in  a  single  day, 
although  the  average  record  is 
very  much  less  than  this. 

Ants.  —  Other  social  Hymen- 
optera  are  the  ants.  The  social 
habits  of  these  insects  have  long 
been  a  subject  of  study.  An 
artificial    ants'    nest    can    easily 


Y/////////////////////y////7\ 


! 


mm 


Food 


\ 


'////////////?//////////////. 


Diagram  ot  an  artificial  ants'  nest; 
S.  moistened  sponge.    After  Miss  Fielde. 


INSECTS  253 

be  made  and  the  whole  colony  studied  in  the  schoolroom  or  at 
home.^ 

Ants  are  the  most  truly  communal  of  all  the  insects.  Their  life 
history  and  habits  are  not  so  well  known  as  those  of  the  bee,  but 
what  is  known  shows  even  more  wonderful  specialization.  The  in- 
habitants of  a  nest  may  consist  of  wingless  workers,  which  in  some 
cases  may  be  of  two  kinds,  and  winged  males  and  females. 

Ant  larvse  are  called  grubs.  They  are  absolutely  helpless  and 
are  taken  care  of  by  nurses.  The  pupae  may  often  be  seen  taken 
out  in  the  mouths  of  the  nurse  ants  for  sun  and  air.  They  are 
mistakenly  called  ants'  eggs  in  this  stage. 

The  colonies  consist  of  underground  galleries  with  enlarged 
storerooms,  nurseries,  etc.  The  ants  are  especially  fond  of  honey- 
dew  secreted  by  the  aphids  or  plant  lice.  Some  species  of  ants 
provide  elaborate  stables  for  the  aphids,  commonly  called  ants' 
cows,  supplying  with  food  and  shelter  and  taking  the  honeydew 
as  their  reward.  This  they  obtain  by  licking  it  from  the  body  of 
the  aphids.  A  western  form  of  ant,  found  in  New  Mexico  and 
Arizona,  rears  a  scale  insect  on  the  roots  of  the  cactus  for  this 
same  purpose. 

It  is  probable  that  some  species  of  ants  are  among  the  most 
warlike  of  any  insects.  In  the  case  of  the  robber  ants,  which  live 
entirely  by  war  and  pillage,  the  workers  have  become  modified  in 

1  A  successful  nest  for  the  schoolroom  is  made  and  described  by  Miss  Adele  M. 
Fielde.     See  the  Biological  Bulletin,  Vol.  VII,  No.  4,  September,  1904. 

The  floor  of  the  nest  is  a  pane  of  window  glass  six  by  ten  inches.  Build  a  wall 
by  cementing  with  crockery  cement  four  half-inch  strips  of  thicker  glass,  and  upon 
these  cement  four  more  strips,  making  the  wall  at  least  one  quarter  of  an  inch  high. 
The  space  inside  is  divided  by  one  or  two  partitions  built  the  same  as  the  outer  wall. 
Spaces  should  be  allowed  for  communication  between  chambers.  The  whole  outer 
surface  of  the  nest  thus  made  may  be  covered  with  black  paper  to  make  it  opaque. 
A  lining  of  Turkish  toweling  is  glued  to  the  top  of  the  wall.  The  cover,  which 
rests  on  the  toweling,  should  be  either  of  glass  made  opaque,  or  better,  of  glass 
(such  as  ruby  glass  of  dark  rooms)  that  will  exclude  most  of  the  ultra-violet  light 
rays.  It  is  best  to  provide  a  separate  roof  for  eacli  chamber.  Ants  need  moisture, 
so  that  a  small  bit  of  moist  sponge  should  be  kept  in  the  room  where  the  ants  live. 
The  food  chamber,  where  bits  of  cake,  banana,  apple,  or  other  food  mixed  with 
honey  or  molasses,  are  placed,  should  also  be  kept  moist. 

To  stock  such  a  nest,  dig  up  a  small  colony  and  transfer  them,  along  with  some 
earth,  to  the  schoolroom.  To  separate  the  ants  from  the  earth  place  them  with  the 
earth  on  a  little  island  of  wood  in  a  basin  of  water.  On  one  side  of  the  island 
place  a  glass  plate  and  shade  this  plate  by  a  piece  of  opaque  paper  raised  slightly 
above  the  glass.  The  ants  soon  remove  themselves  and  their  young  to  the  dark 
area  and  may  then  be  transferred  to  the  nest.  Ant  colonies  have  been  kept  for 
three  or  four  years  in  such  a  nest. 


254 


ZOOLOGY 


Tomato  worm  and  cocoons  of  ichneumons, 
photograph  by  Overton. 


From 


structure,  and  can  no  longer  work,  but  only  fight.  Some  species 
go  further  and  make  slaves  of  the  ants  preyed  upon.  These  slaves 
do  all  the  work  for  their  captors,  even  to  making  additions  to  their 
nest  and  acting  as  nurses  to  their  young. 

The  entire  communal  life  of  the  ants  seems  to  be  based  upon 
the  perception  of  odor.     If  an  ant  of  the  same  species  but  from  a 

different  nest  be  put 
into  another  colony,  it 
will  be  set  upon  and 
either  driven  out  or 
killed.  Ants  never 
really  lose  their  com- 
munity odor ;  those 
absent  for  a  long  time, 
on  returning,  will  be 
easily  distinguished  by 
their  odor,  and  eagerly 
welcomed  by  the  mem- 
bers of  the  nest.  The  talking  of  ants  (when  they  stop  each  other, 
when  away  from  the  nest,  to  communicate)  is  evidently  a  process 
of  smelling,  for  they  caress  each  other  with  the  antennae,  the 
organs  with  which  odors  are 
perceived. 

Ichneumons.  —  One  of  the 
Hymenoptera  (incorrectly 
called  a  fly) ,  the  ichneumon  fly, 
is  of  considerable  importance, 
because  of  its  habit  of  laying 
its  eggs  and  rearing  the 
young  in  the  bodies  of  cat- 
erpillars which  are  harm- 
ful to  vegetation.  Some  of 
the  ichneumons  even  bore 
into  trees  in  order  to  de- 
posit  their   eggs    in    the    larVSe       Thalessa  boring  in  an  ash  tree  to  deposit  its 

of      WOOd-borina;     insects.         It  ^^^^  ^'^  *^^  burrow  of  a  hom-tail  larva,  a 

wood  borer.     From  photograph,  natural 
IS    safe    to     say     that     by    the  size,  by  Davison. 


INSECTS  255 

above  means  the  ichneumons  save  millions  of  dollars  yearly  to  our 
country. 

Reference  Books 

FOR    THE    VVVllj 

Davison,  Practical  Zoology,  pages  52-68.     American  Book  Company. 
Herrick,  Text-book  in  General  Zoology,  Chap.  XV.     American  Book  Company. 
Jordan,   Kellogg,  and  Heath,  Animal  Studies,  Chap.  XXII.     D.   Appleton  and 

Company. 
Needham,  Outdoor  Studies.     American  Book  Company. 

FOR    THE    TEACHER 

Comstock,  Insect  Life.     D.  Appleton  and  Company. 

Lubbock,  Ants,  Bees,  and  Wasps.     D.  Appleton  and  Company. 


XX.     SPIDERS   AND  MYRIAPODS 


Structure  of  the  Spider.  —  Use  any  large  spider  for  the  following  work, 
preferably  Argiope,  the  brightly  colored  garden  spider.* 

Examine  the  large  spider  carefully.  Notice  that  it  differs  from  an  insect 
in  having  the  head  and  thorax  joined  together  to  form  a  cephalothorax. 

Notice  the  number  of  legs; 
here  is  another  difference  from 
insects.  Look  on  the  dorsal 
side  of  the  cephalothorax. 
The  glistening  black  objects 
are  simple  eyes,  of  which  there 
are  usually  four  pairs.  What 
is  the  number  and  position 
of  eyes  in  this  specimen? 
Make  a  diagram.  Argiope 
breathes  by  means  of  lung- 
like sacs  in  the  abdomen,  the 
openings  of  which  can  some- 
times be  seen  just  behind  the 
most  posterior  pair  of  legs. 
Another  organ  possessed  by 
the  spider,  which  insects  do 
not  have  (except  in  a  larval 
form),  is  known  as  the  spin- 
neret. This  is  a  set  of  glands 
which  secrete  in  a  liquid  state 
the  silk  which  the  spider 
spins.  On  exposure  to  air  this  fluid  hardens  and  forms  a  very  tough  build- 
ing material  which  combines  lightness  with  strength.  Look  carefully  at 
a  spider  spinning  and  decide  where  the  spinnerets  are  located. ^ 

Uses  and  form  of  the  Web.  —  The  web-making  instinct  of  spiders 
forms  an  interesting  study.  Our  common  spiders  may  be  grouped  accord- 
ing to  the  kind  of  home  they  build.  The  web  in  some  cases  is  used  as  a 
home,  in  others  it  forms  a  snare  or  trap.  In  some  cases  the  web  is  used 
for  ballooning,  spiders  having  been  noticed  clinging  to  their  webs  miles 
out  at  sea.  The  webs  seen  most  frequently  are  the  so-called  cobwebs. 
These  usually  serve  as  a  snare  rather  than  a  home,  some  species  remain- 
ing away  from  the  web.  In  other  cases  the  spider  hangs,  back  down- 
ward, under  a  thin  sheet  of  filmy  cross  lines. 

The  funnel-web  makers  form  a  closely  woven  web  which  is  usually  attached 
to  grass  or  may  be  found  in  corners  of  a  building.      From  one  end  of  the 

*  For  laboratory  work  see  Hunter  and  Valentine,  Manual,  page  117. 

2  Useful  laboratory  or  home  work  may  be  given  in  the  form  of  tabular  com- 
parisons between  the  various  species  of  "the  arthropods.  For  examples  of  such 
tables  see  Hunter  and  Valentine,  Manual,  pages  116,  120,  127,  130. 

256 


Tarantula  on  its  back;  p,  poison  fang;  s,  spinneret. 
Reduced  from  photograph  by  Davison. 


SPIDERS    AND   MYRTAPODS 


257 


web  a  funnel-like  tube  runs  downward  and  inward.  In  this  tube  the 
spider  spends  most  of  the  time,  running  out  to  catch  insects  which  may  be- 
come entrapped.  At  the  lower  end  of  the  tube  is  an  opening  through 
which  the  spider  may  escape  in  time  of  necessity.  The  funnel-web 
builders  are  strong-legged,  active  spiders. 

The  orb-weaving  spiders  spin  webs  of  geometrical  exactness  in  bushes  or 
long  grass.  They  are  usually  of  almost  circular  form  with  a  spirally  wound 
center  thread  supported  on  guy  lines  which  are  attached  firmly  to  surround- 
ing objects.  These  webs,  which  act  both  as  homes  and  snares,  are  made 
of  two  kinds  of  silk,  a  supporting  thread,  tough  but  rather  inelastic,  and  a 
thinner  elastic  sticky  thread,  out  of  which  the  snare  is  woven.  The  outer 
part  of  the  web  forms  the  snare.  The  central  part  of  the  web  usually  con- 
tains a  shield  of  closely  woven  silk  on  which  the  spider  may  rest.  Some  orb 
weavers  live  near  one  edge  of  the  web,  hanging  suspended  within  easy  reach 
of  a  possible  capture.  In  traveling  over  the  outer  part  of  the  web  the 
spider  uses  the  guy  lines  only,  as  otherwise  it  might  destroy  its  own  web. 
Why? 

One  of  the  commonest  of  the  orb  weavers  is  a  large  yellow  and  black 
spider  known  as  Argiope.  Their  webs  may  be  found  in  almost  any  garden 
or  yard. 

Find  such  a  web.  Describe  its  location.  How  is  it  attached?  How 
many  guy  lines  does  it  contain?     Look  for  the  central  shield  on  which  the 


A  poisonous  centiped  from  Texas.     Half  natural  size.    From  photograph  by  Davison. 

spider  rests.  Do  you  find  a  "winding  stair"?  Notice  the  open  area  be- 
tween the  central  home  of  the  spider  and  the  outer  or  spiral  zone  of  the 
web.  This  area,  known  as  the  free  zone,  gives  opportunity  for  free  move- 
ment around  the  web,  as  the  spider  does  not  travel  on  the  sticky  outer 
portion. 

Other  Forms  of  Web.  —  Other  forms  of  webs  are  seen  in  the  wonderful  nc^st 
of  the  trapdoor  spider  which,  after  excavating  a  hole  in  the  ground,  lines 
it  with  silk  and  then  makes  a  lid  of  earth  also  lined  with  silk.  Tliis  lid  is 
closed  by  the  spider  after  its  retreat  to  the  hole.  Other  spiders  use  the  web 
for  bridge  building.  In  this  case  a  long  single  strand  is  spun  which  is 
allowed  to  float  off  behind  the  spider  into  the  air.      This  is  flown  like  a 

hunter's    BIOL.  17 


258  ZOOLOGY 

kite  until  it  catches  some  projection,  when  the  spider  hauls  in  the  slack, 
makes  it  fast,  and  travels  across  on  the  slender  bridge  thus  built. 

Myriapods.  —  We  are  all  familiar  with  the  harmless  and  common 
thousand  legs  found  under  stones  and  logs.  It  is  a  representative 
of  the  group  of  animals  known  as  the  millepeds.  These  animals 
have  the  body  divided  into  two  regions,  head  and  trunk.  They 
have  two  pairs  of  legs  for  each  body  segment.  The  centipeds,  on 
the  other  hand,  have  only  one  pair  of  legs  to  each  segment.  None 
of  the  forms  in  the  eastern  part  of  the  United  States  are  poisonous. 

Classification  of  Arthropoda 

Class,  Crustacea.     Arthropods  with  limy  and  chitinous  exoskeleton,  breathing  by 

gills,  and  having  two  pairs  of  antennae. 
Subclass  I.     Eniomostraca.     Crustacea   with   a  variable  niimber  of  segments, 

chiefly  small  forms  with  simple  appendages.     Some  degenerate  or  parasitic. 

Examples,  barnacles,  water  flea  (Daphnia),  and  copepods  (Cyclops). 
Subclass  II.     Malacostraca.     Usually  large   Crustacea   ha\ang   nineteen   pairs 

of  appendages.      Examples,   American  lobster  (Homarus  americanus) ,   crab 

(Cancer),  or  shrimp  (Paloemonetes) . 
Class,  Hexapoda  (insects).     Arthropoda  having  chitinous  exoskeleton,  breathing 

by  air  tubes  (tracheae),  and  having  three  distinct  body  regions. 
Order,  Aptera  (without  wings).     Several  wingless  forms.     Examples,  springtails. 
Order,  Orthoptera  (straight  wings).      Example,  Rockj^  Mountain  locust. 
Order,  Lepidoptera  (scale  wings).     Examples,  cabbage  butterfly,  cecropia  moth. 
Order,  Diptera  (two  wings).     Examples,  house  flj',  mosquito. 
Order,  Hemiptera  (half  wing).     Examples,  all  true  bugs,  plant  lice,  and  cicada. 
Order,  Neuroptera  (nerve  wings).     Examples,  May  fly,  dragon  fly. 
Order,  Coleoptera  (shield  wings).     Examples,  beetles. 
Order,  Hymenoptera  (membrane  wings).     Examples,  bees,  wasps,  ants. 
Class,  Arachnida.      Arthropoda   with    head    and    thorax    fused.       Six    pairs    of 

appendages.     No  antennae.     Breathing  by  both  lungs  (spiders)  or  tracheae. 

Examples,  spiders  and  scorpions. 
Class,  Myriapoda.       Arthropoda,    having    long    bodies    with     many    segments ; 

one  or  two  pairs  of  appendages  to  each  segment.     Breathing  by  means  of 

tracheae.     Example,  centiped. 

Referexck  Books 

FOR    THE    PUPIli 

Needham,  Outdoor  Studies,     American  Book  Company. 

FOR    THE    TEACHER 

Emerton,  The  Structure  and  Habits  of  Spiders.     Knight  and  Millet. 


XXI.     MOLLUSKS 


MoUusca.  —  The  name  Mollusca  (Latin  mollis  =  soft)  gives 
the  character  which  chiefly  aids  us  in  identifying  a  mollusk. 
The  body  is  soft  and  unsegmented.  It  is  usually  covered  with  a 
limy  shell,  formed  by  the  agency  of  a  delicate  envelope  called  the 
mantle.  The  animal  usually  possesses  a  single  muscular  foot,  by 
means  of  which  locomotion  takes  place.  There  are  several  groups 
of  mollusks  which  are,  as  we  shall  see,  quite  unlike  in  appearance 
and  in  habits. 

The  Shell  of  the  Fresh-water  Mussel  (Unio  species) }  —  Notice  that  the 
shell  is  made  up  of  two  parts  or  valves.  Such  a  shell  is  called  a  bivalve. 
Notice  that  the  valves  are  joined  together  by  a  structure,  somewhat  elastic, 
called  the  hinge  ligament.  Close  the  two  shells;  why  do  the  shells  spring 
open  again?  The  lines  which  run  more  or  less  parallel  to  the  edge  of  the 
shell  are  called  lines  of  growth.  If  a  line  of  growth  once  represented  the 
outer  edge  of  the  shell,  then 
find  the  oldest  part  of  the 
shell.  This  raised  area  is 
called  the  umbo.  It  is  always 
possible  to  locate  the  anterior 
end  of  the  shell  because  the 
umbo  points  toward  that  end. 
The  hinge  ligament  marks  the 
dorsal  side  of  the  animal. 

The  shell  is  covered  on  the 
outside  by  a  thin  layer  of 
horny  material.  This  is  called 
the  periostracum.  Can  you 
explain  why  it  does  not 
cover  the  entire  shell?  The 
shell  proper,  if  tested  with  acid,  will  be  found  to  contain  considerable 
lime. 

Draw,  natural  size,  a  single  valve,  and  locate  the  hinge  ligament,  umbo, 
and  lines  of  growth.     Place  the  dorsal  surface  upmost  in  the  drawing. 

Mussels  may  be  opened  by  first  placing  the  living  animal  in  hot  water 
until  the  shell  gapes.  Then  insert  a  knife,  keeping  the  blade  close  to  the 
inner  surface  of  one  valve,  cut  through  the  tough  muscles  which  hold  the 
shells  together,  and  the  shells  will  open.  Notice  the  mother  of  pearl  cover- 
ing the  inner  surface.  Notice  in  a  freshly  opened  clam  that  a  delicate 
membrane,  the  mantle,  adheres  to  the  shell. 

Structure  of  Shell. — The  shell,  if  examined  in  cross  section  with  a  good 
lens,  is  seen  to  be  made  up  of  three  layers :  the  outer  periostracum,  made 

*  See  Hunter  and  Valentine,  Manual,  page  138,  for  exercise  on  Venus  Mercenaria. 

259 


Shell  of  fresh-water  clam,  the  left  half  polished  to 
show  the  prismatic  layer. 


260 


ZOOLOGY 


M 


Vertical  section  of  shell  and  mantle  of  a  mollusk; 
C,  periostracum;  P,  prismatic  layer;  L,  laminated 
layer;  S,  shell;  M,  mantle.     (After  Claus.) 


up  of  material  much  like  that 
which  forms  a  cow's  horn,  or 
chitin ;  a  middle  layer  composed 
of  tiny  prisms  of  lime  held  in 
by  the  horny  material  (this 
layer  is  called  prismatic  layer) ; 
and  an  inner  layer  (the  lami- 
nated layer),  made  up  of  layers 
of  lime  and  horn  alternating 
parallel  to  the  surface  of  the 
shell.  The  inner  layer  is  formed 
by  the  action  of  the  whole  sur- 
face of  the  mantle.  The  two 
outer  layers  are  made  by  the 
edge  of  the  mantle  only.  So  a 
shell  grows  in  thickness  largely 
from  the  inner  surface  of  the 
mantle,  while  it  grows  in  diam- 
eter from  the  edge  of  the  mantle 
only. 

The  Open  Shell.  — 'PuU  the 
shells  completely  open.  Find 
on  the  dorsal  side  projections 
and  grooves  which  fit  into  each 
other  when  the  shell  is  closed.  These  are  the  hinge  teeth.  Compare  the 
number  in  each  shell.  How  might  they  be  of  use  to  the  animal?  Find 
the  marks  on  the  shell  where  the  adductor  muscles  were  fastened.  What 
was  the  use  of  the  adductor  muscles  ?  Why  do  dead  mussels  always  have 
the  shell  partly  open  ? 

Draw  one  opened  valve  showing  all  above  parts.     Label  the  anterior  and 
posterior  adductor  muscle  scars,  according  to  position. 

Body  and  Mantle  Cavity.  —  In  one  valve  lies  the  body  of  the  clam.  If  we 
remove  the  mantle,  we  shall  find  under  a  roundish  soft  mass,  the  body,  or 
visceral  mass.  Surrounding  the  visceral  mass  but  ventral  to  it  is  a  cav- 
ity bounded  on  the  outside  by  the  inner  surface  of  the  mantle.  This  is 
the  mantle  cavity.  In  life  this  cavity  is  full 
of  water.  See  if  you  can  discover  how  and 
where  water  gets  in.  In  a  living  mussel  the 
posterior  edge  of  the  mantle  on  the  right 
side  is  folded  so  as  to  fit  with  the  adjoining 
edge  of  the  mantle  on  the  left  side.  The 
funnel-like  openings  thus  formed  are  called 
siphons. 

Siphons.  —  The  siphons  can  best  be  seen 
in  living  mussels  which  have  been  left  quiet 
for  some  time  in  an  open  trough  or  tank.  If 
a  little  powdered  carmine  is  allowed  to  drop 
from  a  medicine  dropper  close  to  the  siphons 
(the  fringed  edges  of  which  may  be  seen  ex- 
tending from  the  shell),  a  current  of  water 
will  be  seen  to  draw  in  and  expel  the  car- 
mine grains.  Where  is  the  incurrent  siphon 
with  reference  to  the  excurrent?  (In  the  Cross  section  of  a  mollusk;  .4.  mantle 
"long-necked"  or  "soft"  clam  the  siphons  cavity;  o,  shell;  6,  gills;  5,  cloacal 
are   greatly   developed    and    are    made   of         cavity;  k,  body. 


MOLLUSKS 


2G1 


tough  muscles  If  they  are  cut  lengthwise,  the  two  tubes,  incurrent  and 
excurrent,  can  be  easily  seen.)  The  siphon  permits  water,  bearing  food 
m?^^^^f^'  ^°rf ^*  ^^^^  *^®  mantle  cavity.  Here  are  found  the  gills 
I  he  Gills.  — The  gills  are  striated  platelike  structures  lying  on  each  side 
of  the  visceral  mass.  How  many  gills  on  each  side?  4ny  difference  in 
size  of  those  on  one  side?  When  the  clam  is  in  a  natural  position,  the 
gills  hang  freely  in  the  mantle  cavity.  In  structure  each  gill  is  a  long  narrow 
bag  open  on  the  dorsal  side.  This  baglike  opening  leads  into  a  second 
cavity,  dorsal  to  the  mantle  cavity.  This  space,  called  the  cloacal  cavity 
is  in  communication  with  the  outside  through  the  excurrent  siphon  A 
mussel  when  viewed  from  one  end  or  in  cross  section  somewhat  resembles 
a  book.  The  shell  has  the  position  of  the  board  cover,  the  mantle  the 
paper  pasted  to  its  inner  surface,  the  gills  the  fly  leaves,  and  the  bodv 
the  printed  pages  in  the  book. 


A  fresh- water  mussel  with  the  right  valve,  mantle,  and  gills  and  some  tissue  at  the  base  of 
the  foot  removed  ;  a,  anterior  adductor  muscle ;  au,  auricle  of  the  heart ;  ft,  foot ;  g,  repro- 
ductive gland  ;  gl,  gill  ;  i,  intestine  ;  k,  kidney ;  m,  mantle ;  n,  nerve  ganglia  connected  by 
nerve  cords  o ;  p,  posterior  adductor  ;  pi,  labial  palps  ;  si,  siphon ;  v,  ventricle.  The  dark 
lines  on  the  mantle  and  foot  are  blood  vessels.    Davison,  Zoology. 


Circulation  of  Water  over  Gills.  —  We  have  already  observed 
that  a  more  or  less  constant  circulation  of  water  takes  place; 
carmine  entering  through  the  incurrent  siphon  passes  out  through 
the  excurrent  siphon.  How  is  this  circulation  explained?  If  a 
sniall  piece  of  the  gill  of  a  clam  or  oyster  is  placed  in  a  drop  of 
the  fluid  found  in  the  mantle  cavity  and  examined  under  the 
compound  microscope,  the  explanation  is  found.  The  surface  of 
the  gill  is  seen  to  be  pierced  by  numerous  holes.     These  holes, 


262  ZOOLOGY 

and  most  of  the  surface  of  the  gill,  are  lined  with  ciliated  cells, 
the  cilia  of  which,  beating  more  strongly  toward  the  cloacal  cavity, 
cause  a  current  of  water  to  flow  over  the  gills  and  through  the 
holes  into  the  cloacal  cavity.  Cilia  are  also  found  lining  the  inner 
surface  of  the  mantle  and  on  the  labial  palps,  which  we  shall 
take  up  later. 

Structure  of  Gills.  —  The  internal  structure  of  the  gills  is  such 
that  blood  slowly  circulates  through  a  network  of  thin-walled 
spaces,  which,  in  the  margin  of  the  gill,  are  separated  from  the 
water  by  only  a  single  layer  of  thin  cells.  Through  this  layer 
oxygen  is  taken  by  osmosis  from  the  water,  and  carbon  dioxide 
given  up.  The  latter  gas  is  passed  off  in  the  water  through  the 
excurrent  siphon. 

Food  Getting.  —  The  cilia  of  the  gills  (and  of  the  mantle  cavity 
in  general)  play  an  important  part  in  food  getting.  The  clam, 
because  of  its  sedentary  life,  must  receive  its  food  in  the  water 
which  enters  the  mantle  cavity.  Food  consists  principally  of  one- 
celled  animals  and  plants.  This  food  is  collected  by  the  cilia  sur- 
rounding the  ostia,  or  holes  in  the  gills,  and  is  passed  to  the  lahial 
palps,  four  little  flaps  which  surround  the  mouth.  The  mouth 
may  be  found  at  the  anterior  end  of  the  visceral  mass.  The  ciliated 
palps  act  as  lips  and  pass  the  food  on  into  the  mouth. 

Food  Tube.  —  The  food  tube  and  its  digestive  gland  (the  latter  a  greenish 
mass  easily  seen  through  the  body  wall)  occupies  part  of  the  visceral  mass. 
It  is  a  thin-walled  tube  which  makes  several  turns  before  leaving  the  body. 
The  stomach  is  a  slight  enlargement  surrounded  by  the  dark-colored  diges- 
tive gland.  This  gland  has  the  same  function  as  the  pancreas  of  higher 
animals. 

Circulation  of  Blood.  —  The  circulation  of  the  blood  in  the  clam 
is  of  chief  interest  to  us  because  of  the  curious  heart,  which  is 
well  developed,  and  has  somewhat  the  same  action  as  in  the 
higher  animals.  The  heart  may  easily  be  found  in  a  living  clam 
and  the  rate  of  beating  counted.  It  is  located  near  the  surface 
of  the  dorsal  side  of  the  body  close  to  the  hinge  ligament.  It 
consists  of  two  chambers,  an  auricle,  which  receives  the  blood, 
and  a  ventricle,  which  by  muscular  contraction  pumps  the  blood 
on  its   course.      The    heart    is    surrounded    by   a    thin-walled 


MOLLUSKS  263 

pericardium  or  sack.     The  intestine  passes  directly  through  the 
heart,  a  condition  found  in  no  other  group  of  animals. 

Locomotion.^  —  Locomotion  may  be  observed  if  mussels  are 
kept  in  an  aquarium.  The  fleshy  foot  is  thrust  down  into  the 
mud  or  sand  and  then  contracted.  This  action  pulls  the  clam 
forward  for  a  short  distance.     Locomotion  is  thus  very  slow. 

The  Nervous  System.  —  Although  the  mussel  appears  to  have  no  organs 
of  sight  or  hearing,  yet  it  is  provided  with  a  complicated  nervous  system 
which  appears  to  have  much  to  do  with  muscular  activity.  Three  large 
collections  of  nerve  cells  (called  ganglia)  are  found,  one  near  each  adductor 
muscle  and  one  near  the  foot  (see  diagram). 

Early  Development. — The  early  life  history  of  most  mollusks  includes 
a  free-swimming  stage  before  the  young  possess  a  shell.  At  this  time  the 
tiny  larva  swims  by  means  of  cilia,  near  the  surface  of  the  water.  The 
fresh-water  mussel  at  an  early  stage  attaches  itself  to  the  gills  of  a  fish, 
thus  living  for  a  time  as  a  paraisite.  Eventually  all  bivalve  mollusks  come 
to  live  near  the  bottom,  where  they  are  near  a  source  of  food  supply. 

The  Oyster.  —  The  chief  difference  between  the  oyster  and  the 
clam  lies  in  the  fact  that  the  oyster  is  fastened  by  one  valve  to 
some  solid  object,  while  the  clam  and  the  fresh  water  mussel  move 
about.     This  results  in  an  asymmetry  in  the  shell  of  the  oyster. 

Oysters  are  never  found  in  muddy  localities,  for  in  such  places 
they  would  be  quickly  smothered 
by  the  sediment  in  the  water.  They 
are  found  in  nature  clinging  to 
stones  or  on  shells  or  other  objects 
which  project  a  little  from  the  bottom. 
Here  food  is  abundant   and  oxygen  is 

,  Shell  of  oyster,  snowing  asymmetry. 

obtained  from  the  water  surroundmg 

them.     Hence  oyster  raisers  throw  oyster  shells  into  the  water  to 

hold  the  young  off  the  muddy  bottom. 

In  some  parts  of  Europe  and  this  country  where  oysters  are 
raised  artificially,  stakes  or  brush  are  sunk  in  shallow  water  so 
that  the  young  oyster,  which  is  at  first  free-swimming,  may  escape 
the  danger  of  smothering  on  the  muddy  bottom. 

After  the  oysters  are  a  year  or  two  old  they  are  taken  up  antl 
put  down  in  deeper  water  as  seed  oysters.     At  the  age  of  three 

1  See  Hunter  and  Valentine,  Manual,  page  142. 


264 


ZOOLOGY 


and  four  years  they  are  ready  for  the  market.  Sometimes  oysters 
are  artificially  fattened  by  placing  them  on  beds  near  the  mouths 
of  fresh  water  streams.  Too  often  these  streams  are  the  bearers 
of  much  sewage,  and  the  oyster,  which  lives  on  microscopic 
organisms,  takes  in  a  number  of  bacteria  with  other  food.  Thus 
a  person  might  become  infected  with  the  typhoid  bacillus  by  eat- 
ing raw  oysters. 

The  oyster  industry  is  one  of  the  most  profitable  of  our  fisher- 
ies. Nearly  $30,000,000  a  year  has  been  derived  during'  the  last 
decade  from  such  sources.  Hundreds  of  boats  and  thousands  of 
men  are  engaged  in  dredging  for  oysters.  Some  of  the  most 
important  of  our  oyster  grounds  are  Long  Island  Sound  and 
Chesapeake  Bay. 

Clams.  —  Other  bivalve  mollusks  used  for  food  are  clams  and 
scallops.     Two  species  of  the  former  are  known  to  New  Yorkers, 

one  as  the  ''  round," 
another  as  the  ''  long  " 
or  ''  soft -shelled  " 
clams.  The  former 
( Venus  Merceneria) 
was  called  by  the  In- 
dians quahog,  and  is 
still  so  called  in  the 
Eastern  States.  The 
blue  area  of  its  shell 
was  used  by  the  In- 
dians as  wampum,  or 
money.  The  quahog 
is  now  extensively  used 
as  food.  The  "  long  " 
clam  (Mya  arenaria) 
is  considered  better 
eating  by  the  inhabit- 
ants of  Massachusetts 
and  Rhode  Island.  This  clam  was  highly  prized  as  food  by 
the  Indians.  The  long  siphon,  incorrectly  called  neck,  enables 
these  clams  to  burrow  deep  into  the  mud  and  yet  take  food  and 


Round  clam  {Venus  Merceneria);  A. A.M.,  anterior  ad- 
ductor muscle;  A.R.M.,  anterior  retractor  muscle; 
P.A.M.,  posterior  adductor  muscle;  P.R.M.,  posterior 
retractor  muscle;  F.,  foot;  C,  cloacal  chamber;  I.S.,  in- 
current  siphon;  F.S.,  excurrent  siphon;  EO.,  heart; 
G.,  gills;  M.,  mantle;  Z).GL.,  digestive  glands;  S., 
stomach;  /.,  intestine;  P.,  palp;  R.,  posterior  end  of 
digestive  tract. 


MOLLUSKS 


265 


oxygen  from  the  water  above.     The  clam  industries  of  the  eastern 
coast  aggregate  over  $1,000,000  a  year. 

Scallop.  —  The  scallop,  another  highly  esteemed  mollusk,  forms 
an  important  fishery.  The  scallop  rests  on  one  valve  on  the 
bottom  in  shallow  water  and  if 
disturbed  swims  away  by  clapping 
the  valves  rapidly  together.  The 
single  adductor  muscle  is  eaten, 
whereas  in  the  clam  the  soft  parts 
of  the  body  are  used  as  food. 


i''ulgur,  a  univalve  rnollusk  common  in 
Long  Island  Sound,  which  does  much 
harm  by  boring  into  the  shells  of  edible 
moUusks. 


A  Univalve  Shell.  —  Any  large  uni- 
valve shell,  as  Fulgur,  may  be  used  in 
the  laboratory.^      The  shell,  which  is 
one  piece,  is  called  a  univalve.    Notice 
the  spiral  arrangement   of   the  shell. 
How- many  turns  does  it  make?     The 
lines  of  growth  run  parallel,  as  in  the  clam,  to  the  edge  of  the  shell.     Hold 
the  openmg  toward  you.     The  opening  is  known  as  the  aperture.     When 
the  animal  is  alive,  part  of  the  body  is  protruded  through  this. 
Draw  the  shell  twice  natural  size,  showing  all  above  parts. 

Living  Snail.  —  (Use  the  pond  snail 
Limnea  or  Physa.)  Watch  the  move- 
ment of  living  snails  in  the  aquarium. 
The  large  fleshy  mass  which  protrudes 
from  the  shell  is  called  the  foot.  Try 
to  decide  how  locomotion  takes  place 
as  the  animal  moves  along  the  side 
of  the  acfuarium. 

Watch  the  animal  as  it  feeds.  What 
kind  of  food  docs  this  snail  eat? 
Notice  the  position  of  the  mouth.  Is 
there  any  distinct  head?  These  ani- 
mals are  called  gastropodss  (stomach- 
footed).  Do  you  see  any  reason  for 
this  name?  P'ind  the  two  tentacles 
or  horns.  Touch  them  with  a  pencil. 
What  happens?  Look  for  the  dark 
eye-spots  at  the  base  of  th.e  tentacles. 
Make  any  experiments  you  can  to  see 
if  the  snail  can  distinguish  between 
light  and  darkness.  (Cover  part  of 
the  dish  and  Ica^e  it  for  some  minutes 
undisturbed.)  Do  you  find  any  other 
structures  protruding  from  the  edge  of  the  foot  ?  Two  siphons,  one  for  tak- 
ing in  water,  the  other  for  sending  it  out,  may  be  found. 

Gastropods. — Snails,  whelks,  slugs,  and  the  like  arc  called  gastropods 
because  the  foot  occupies  so  much  space  that  most  of  the  organs  of   the 

1  See  Hunter  and  Valentine,  Manual,  pages  143  antl  145. 


■■ 

n 

vl 

^#1 

y 

p 

Hi    ^J^^H 

^^^f     '  r  j^^^^^  ^^^HB 

Q 

■               ^■B            '^^H 

Strophia.s  from  different  localities  at  An- 
dros  and  New  Providence,  Bahamas. 
From  photograph  loaned  by  the  Ameri- 
can Museum  of  Natural  History. 


266 


ZOOLOGY 


Forest  snail,  showing  the  two 
tentacles  with  an  eye  on 
the  end  of  each.  From 
photograph  by  Davison. 


-Wfeo^^Hti -'t 


body,  including  the  stomach,  are  covered  by  it. 

^^■^^^        ^jT  In  most  gastropods  the  body  is  spirally  twisted  in 

^^^B^^jjtKt^-^         the  shell.     In  the  garden  slug,  the  mantle  does  not 

^^^B^^^^^^  secrete  a  shell  and  the  naked  body  is  symmetri- 

^^^^^m  cal.     The  twisting  of  the  body  is  not  seen  in  very 

■HgT  young  snails,  so  that  this  peculiar  state  is  believed 

to  be  something  secondar}'"  which  has  appeared  as 
a  consequence  of  the  animal's  bearing  a  shell. 

Variability  of  Snail  Shells.  —  Snail  shells 
arc  very  variable  in  shape  and  color  markings,  as 
may  be  seen  if  several  of  the  same  species  be  ex- 
amined carefully.  Varieties  of  snails  in  mountain 
valleys  in  certain  of  the  Hawaiian  Islands  are  found  to  be  quite  distinct, 
each  in  its  own  valley.  Yet  it  is  quite  certain  that  all  the  snails  of  these 
several  varieties  were  at  one  time  alike.  Helix  nemoralis,  a  European 
snail,  has  been  introduced  into  this  country  and  has  multiplied  so  rapidly 
and  varied  so  greatly  that  in  an  area  one  thousand  feet  in  diameter  three 
hundred  and  eighty-five  varieties  have  been  collected,  each  slightly  differing 
from  the  other  either  in  color  or  form  of  shell. ^ 

Feeding  Habits.  —  The  mouth  of  the  snail  is  easily  found  on  the  under 
side  of  the  foot.  Just  within 
the  mouth  is  the  lingual  rib- 
bon. The  ribbon  consists  of  a 
flap  of  membrane  bearing 
many  sharp,  filelike  teeth, 
microscopic  in  size.  This 
structure,  which  is  moved  by 
muscles,  passes  over  a  pad  of 
cartilage  and  rubs,  filelike, 
against  the  surface  to  which  it 
is  applied.  In  this  manner 
some  snails  can  bore  circular 
holes  in  shells  of  other  mol- 
lusks,  in  order  to  get  the  soft 
part,  which  they  use  as  food. 
An  example  of  a  univalve 
moUusk  which  thus  obtains 
food  is  the  oyster  drill,  which 
annually  does  thousands  of 
dollars'  worth  of  damage  to  the 
oysters.  In  Europe  and  this 
country  slugs  and  some  snails  do  considerable  damage  to  gardens  by  eat- 
ing young  plants.      The  snail  Physa  may  be  observed  feeding   on  tiny 

^  See  Howe,  Amer.  Nat.,  December,  1898. 


%N. 


•  "i 


0    . 


Shell  full  of  holes  bored  by  the  oyster  drill  and  a 
boring  sponge. 


MOLLUSKS 


267 


plants  on  the  surface  of  the  aquarium  and  the  action  of  the  hngual  ribbon 
noted. 

Breathing.  —  Most  gastropods  breathe;  by  means  of  gills  which  are  lo- 
cated, as  in  the  clam,  in  the  mantle  cavity.  But  in  some  snails,  the 
pulmonates,  the  mantle  cavity  forms  a  sac  which  opens  to  the  outside  of  the 
body  by  a  tiny  slit.  In  this  cavity  air  is  taken.  Its  walls  are  filled  with 
blood  vessels,  and  oxygen  is  then  taken  up  by  the  blood  as  carbon  dioxide 
is  released.  The  pulmonates  are  true  air  breathers,  and  may  frequently  be 
seen  in  an  aquarium  taking  down  a  bubble  of  air  for  use  under  water. 

Senses.  —  Snails  and  slugs  can  distinguish  light  from  darkness,  as  may  be 
easily  proved  by  experiment.  The  tentacles  are  the  most  sensitive  parts  of 
the  body.  Certain  parts  of  the  animal  seem  to  be  used  for  testing  the  water, 
and  in  the  land  snails  these  organs  seem  to  be  used  to  smell  with.  The 
nervous  system  as  in  the  clam  consists  of  three  collections  of  nerve  cells,  or 
ganglia,  nerves  connecting  these  centers,  and  numerous  cells  in  the  outer 
part  of  the  body  called  sensory  cells.  These  cells  are 
sensitive  to  any  stimulus  received  from  outside  the 
body. 

Development.  —  Eggs  of  the  pond  snails  are  laid  in 
little  masses,  sometimes  in  strings,  and  are  often  found 
fastened  in  a  jelly  to  the  side  of  the  aquarium.  The 
snails  hatch  and  at  first  swim  about,  later  settling 
down  as  the  shell  is  formed.  Thus  they  undergo  a 
complete  metamorphosis,  as  do  their  relatives  the  clams 
and  oysters. 

Cephalopods.  —  Squid,  Cuttlefish,  and  Octopus.  The 
name  cephalopod  means  head-footed.  As  the  figure 
shows,  the  mouth  is  surrounded  with  a  circle  of  ten- 
tacles. The  shell  is  internal  or  lacking,  the  so-called 
pen  of  the  cuttlefish  being  all  that  remains  of  the  shell. 
The  squid,  or  cuttlefish,  is  strangely  modified  for  the 
hfe  it  leads.  It  moves  through  the  water  more  swdftly 
than  a  fish  by  squirting  water  from  the  siphon.  It  can 
seize  its  prey  with  the  suckers  on  the  long  tentacles 
and  tear  it  in  pieces  by  means  of  its  horny  parrotlike 
beak.  It  is  protected  from  its  enemies  and  is  enabled 
to  catch  its  prey  because  of  its  ability  to  change  color  ^^"JJJ 
quickly.  This  change  of  color  is  caused  by  the  move- 
ment of  certain  color-bearing  cells  under  the  skin.  In 
this  way  the  animal  simulates  its  surroundings.  The  cuttlefish  has  an  mk 
bag  near  the  siphon  which  contains  the  black  sepia.  A  few  drops  of  this  ink 
squirted  into  the  water  effectually  hide  the  animal  from  its  enemy. 

To  this  group  of  animals  belongs  also  the  octopus,  or  devil  fish,  a  ceph- 
alopod known   to  have  tentacles  over  thirty  feet  in  length.     The  paper 


id.    One  fourth 
ral   size.      Da- 
vison, Zoology. 


268  ZOOLOGY 

nautilus  and  pearly  nautilus,  the  latter  made  famous  by  our  poet  Holmes, 
also  belong  to  this  group. 


Octopus. 

Habitat  of  the  MoUusks.  —  Mollusks  are  found  in  almost  all 
parts  of  the  earth  and  sea.  They  are  more  abundant  in  temperate 
localities  than  elsewhere,  but  are  found  in  tropical  and  arctic 
countries.  They  are  found  in  all  depths  of  water,  but  by  far  the 
greatest  number  of  species  live  in  shallow  water  near  the  shore. 
The  cephalopods  live  near  the  surface  of  the  ocean,  where  they 
prey  upon  small  fish.  The  food  supply  evidently  determines  to  a 
large  extent  where  the  animal  shall  live.  Some  mollusks  are 
scavengers,  others  feed  on  living  plants. 

We  have  found  in  the  forms  of  Mollusc  a  studied  that  almost  all 
mollusks  live  in  the  water.  There  is  one  great  group  which  forms, 
a  general  exception  to  this,  certain  of  the  snails  and  slugs  called 
pulmonates.  But  even  these  animals  are  found  in  damp  localities, 
and  at  the  approach  of  drought  they  become  inactive,  remaining 
within  the  shell.  The  European  snail  {Helix  pomatia),  imported 
to  this  country  as  a  table  delicacy,  exists  for  months  by  plugging 
up  the  aperture  to  the  shell  with  a  mass  of  slimy  material  which 
later  hardens,  thus  protecting  the  soft  body  within. 

Economic  Importance.  —  In  general  the  mollusks  are  of  much 
economic  importance.     The  bivalves  especially  form  an  important 


MOLLUSKS 


269 


source  of  our  food  supply.  Many  of  the  mollusks  also  make  up 
an  important  part  of  the  food  supply  of  bottom-feeding  fishes. 
On  the  other  hand, 
some  mollusks,  as  A^a- 
tica,  bore  into  other 
mollusk  shells  and  eat 
the  animal  thus  at- 
tached. Some  boring 
mollusks,  for  example 
the  ship  worm  ( Teredo 
navalis),  do  much 
damage,  especially  to 
wharves,  as  they  make 
their  home  in  piles. 
Still  others  bore  holes 
in  soft  rock  and  live 
there. 

The  shells  of  mollusks  are  used  to  a  large  extent  in  manufacture 
and  in  the  arts,  while  they  form  a  money  basis  still  in  parts  of 
the  world.     Sepia  comes  from  a  cuttlefish. 

Pearls  and  Pearl  Formation.  —  Pearls  are  prized  the  world  over.  It  is 
a  well-known  fact  that  even  in  this  country  pearls  of  some  value  are  some- 
times found  within  the  shells  of  such  common  bivalves  as  the  fresh-water 
mussel  or  oyster.  Most  of  the  finest,  however,  come  from  the  waters  around 
Ceylon.  If  a  pearl  is  cut  open  and  examined  carefully,  it  is  found  to  be 
a  deposit  of  the  mother-of-pearl  layer  of  the  shell  around  some  central 
structure.  It  has  been  believed  that  any  foreign  substance,  as  a  grain  of 
sand,  might  irritate  the  mantle  at  a  given  point,  thus  stimulating  it  to 
secrete  around  the  substance.  It  now  seems  likely  that  perfect  pearls  are 
due  to  the  growth  within  the  mantle  of  the  clam  or  03^stcr  of  certain  para- 
sites, stages  in  the  development  of  a  fluke  worm.  The  irritation  thus  set 
up  in  the  tissue  causes  mother-of-pearl  to  be  deposited  around  the  source 
of  irritation,  with  the  subsequent  formation  of  a  pearl. 


Piece  of  timber,  showing  holes  bored  by  the  ship  worm. 


Classification  op  Molt.ttsks 

Class  I.  Pelecypoda  (Lamellibranchiata).  Soft-bodied  unsegmented  animals 
showing  bilateral  symmetry.  Bivalve  shell,  platelikc  gills.  Examples, 
clam  (Mya  arenaria),  scallop  ipecten),  oyster  (Ostrea),  and  fresh-water  mussel 
{JJnio), 


270  ZOOLOGY 

Class  II.  Gastropoda.  Soft  bodies  asymmetrical ;  imivalve  shell  or  shell  absent 
Some  forms  breathe  by  gills,  others  by  Imiglike  sacs.  Examples,  pond  snail, 
land  snail  {Helix),  and  slug. 

Class  III.  Cephalopoda.  Bilaterally  symmetrical  mollvisks  with  mouth  sur- 
rounded by  tentacles.  Shell  may  be  external  (nautilus),  internal  (squid),  or 
altogether  lacking  (octopus) .     Examples,  squid,  octopus. 

Reference  Books 

for  the  pupil 

Davison,  Practical  Zoology,  pages  142-150.     American  Book  Company. 
Herrick,  Text-hook  in  General  Zoology,  Chap.  XI.     American  Book  Company. 
Heilprin,  The  Animal  Life  of  our  Seashore.     J.  B.  Lippincott  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies.     D.  Appleton  and  Company. 
Morgan,  Animal  Sketches,  Chap.  XXI.     Longmans,  Green,  and  Company. 

FOR   THE    TEACHER 

Bulletin,  U.S.  Fish  Commission,  1889. 

Brooks,  The  Oyster.     Johns  Hopkins  Press. 

Cooke,  The  Mollusca,  Cambridge  Natural  History.     The  Macmillan  Company. 

Kellogg,  The  Life  History  of  the  Common  Clam.     Bulletin,  U.S.  Fish  Commission 

Vol.  XIX,  page  193. 
Parker,  Elementary  Biology.     The  Macmillan  Company. 
Parker  and  Haswell,  Text-hook  of  Zoology.     The  Macmillan  Company. 


XXII.    FISHES 

The  ordinary  stickleback  is  a  hardy  fish  easily  kept  in  aquaria 
in  the  schoolroom.  It  (or  any  other  small  fish,  as  the  brook 
minnow  or  goldfish)  may  be  used  in  the  following  exercise.^ 

The  Body. — The  body  of  the  fish  runs  insensibly  into  the  head,  the  neck 
being  absent.  Notice  the  long,  narrow  body.  How  is  it  adapted  for  the 
method  of  hfe?  Certain  cells  in  the  skin  secrete  mucus  or  slime.  How 
might  the  slimy  surface  of  the  body  be  useful  to  the  fish  ?  If  the  fish  is  in 
an  aquarium  with  surroundings  like  that  of  its  natural  habitat,  decide 
whether  the  color  of  the  fish  is  protective. 

The  Appendages  and  their  Uses.  —  The  appendages  of  the  fish  consist  of 
paired  and  unpaired  fins.  The  paired  fins  are  four  in  number,  and  are  be- 
lieved to  be  homologous  with  the  paired  limbs  of  a  man.  Compare  the  fish 
with  the  diagram  in  the  book  and  locate  the  paired  pectoral  and  pelvic  fins. 
(These  are  so  called  because  they  are  attached  to  the  bones  forming  the 
pectoral  and  pelvic  girdles.  See  page  275.)  Find,  by  comparison  with 
th6  diagram,  the  dorsal,  anal,  and  caudal  fins.     How  many  unpaired  fins? 


The  fins  of  a  fish;  A,  dorsal;  B,  caudal;  C,  anal;  D,  pelvic;  E,  pectoral. 

The  stickleback,  as  the  name  indicates,  has  the  front  dorsal  fin  so  modi- 
fied as  to  form  a  number  of  sharp  spines.  (There  are  five  in  the  common 
brook  stickleback  of  New  York  state.)  A  careful  study  of  a  fi.^h  in  the 
school  aquarium  will  help  to  an  understanding  of  the  uses  of  the  diflFer- 
ent  fins.  Decide  what  part  in  the  locomotion  of  the  fi.sh  is  taken  by  the 
caudal  fin.  Do  the  other  fins  function  in  forward  movement?  Which  fins 
are  used  in  turning?  In  backing?  Are  any  used  in  balancing?  Do  any 
parts  of  the  body  play  a  part  in  locomotion  ? 

1  See  Hunter  and  Valentine,  Manual,  page  167. 

271 


272 


ZOOLOGY 


The  Senses.  —  Notice  the  position  of  the  eyes  from  the  front  and  in  a 
side  view  of  the  fish.  Is  the  position  of  advantage  and  how?  The  eye  is 
globular  in  shape.  Such  an  eye  has  been  found  to  be  very  near  lighted. 
Thus  it  is  unlikely  that  a  fish  is  able  to  perceive  objects  at  any  great  dis- 
tance from  it.  The  eye  is  unprotected  by  eyelids,  but  the  position  on  the 
sides  of  the  body  affords  some  protection.  There  is  much  opportunity  for 
a  careful  boy  or  girl  to  make  simple  experiments  to  determine  how  much 
and  how  far  the  fish  can  see. 

Feed  the  fish;  does  it  appear  to  see  the  food  or  to  go  to  the  food  by  a 
sense  of  smell?  The  nostrils  of  a  fish  can  be  proved  to  end  in  little  pits, 
one  under  each  nostril  hole.  Thus  they  differ  from  our  own,  which  are 
connected  with  the  mouth  cavity.  In  the  catfish,  for  example,  the  barbels 
or  horns  receive  sensations  of  smell  and  taste.  The  sense  of  perceiving 
odor  is  not  as  we  understand  the  sense  of  smell,  for  a  fish  perceives  only 
substances  that  are  dissolved  in  the  water  in  which  it  lives.  The  senses  of 
taste  and  touch  appear  to  be  less  developed  than  the  other  senses.  A  fish 
rejects  bits  of  food  which  it  does  not  like. 

Breathing.  —  Notice  that  a  fish,  when  swimming  quietly  or  when  at  rest, 
seems  to  be  biting  when  no  food  is  present.  A  reason  for  this  act  is  to  be 
seen  when  we  introduce  a  little  finely  powdered  carmine  into  the  water 
near  the  head  of  the  fish.  It  will  be  found  that  a  current  of  water  enters 
the  mouth  at  each  of  these  movements  and  passes  out  through  two  slits 
found  on  each  side  of  the  head  of  the  fish.     Investigation  shows  us  that 

under  the  broad,  flat  plate  or 
operculum  forming  each  side  of 
the  head  lie  several  long,  feathery, 
red  structures,  the  gills. 

Gills.  —  If  we  examine  the 
gills  of  any  large  fish ,  we  find  that 
a  single  gill  is  held  in  place  by  a 
bony  arch,  made  of  several  pieces 
of  bone  which  are  hinged  in  such 
a  way  as  to  give  great  flexibility 
to  the  gill  arch,  as  the  support  is 
called.  Covering  the  bony  frame- 
work, and  extending  into  the 
throat,  are  a  series  of  delicate 
filaments  of  flesh,  covered  with  a 
very  delicate  membrane  or  skin. 
Into  each  of  these  filaments  pass 
two  blood  vessels,  one  downward 
and  one  upward.  Blood  reaches 
the  gills  and  is  carried  away  from 
tht;se  organs  by  means  of  two  large 
vessels  which  pass  along  the  bony 
arch  previously  mentioned.  Blood  passes  into  the  gill  filament,  and  there 
comes  in  contact  with  the  free  oxygen  of  the  water  bathing  the  gills.  An  ex- 
change of  gases  through  the  walls  of  the  gill  filaments  results  in  the  loss  of 
carbon  dioxide  and  a  gain  of  oxygen  by  the  blood.  Possibly  other  waste 
products  find  their  way  into  the  water  bathing  the  gill  filaments,  the  wastes 
being  carried  off  by  the  current  of  water  passing  over  the  gills. 

Teeth.  —  Notice  the  arrangement  and  number  of  the  teeth  in  the  stickle- 
back. Sticklebacks  are  carnivorous,  preying  upon  the  eggs  and  young  of 
other  small  fish  inhabiting  the  brooks  where  they  live.  They  also  feed 
upon  decaying  and  live  vegetable  matter,  especially  algae.     The  teeth  of 


Gills  and  heart  of  the  fish,  exposed  by  removal 
of  gill  cover  on  left  side;  a,  first  of  the  four 
bony  arches  which  carry  the  gills ;  b,  gills ; 
b',  lower  edges  of  gills  on  the  right  side; 
h,  heart. 


THE   FISHES 


273 


the  stickleback  are  small  and  evidently  useful  for  seizing  and  holding  prey. 
This  fish,  like  many  other  specie's,  is  a  hunter  and  uses  the  teeth  as  weap- 
ons of  offense  as  well  as  for  defense.  How  are  the  teeth  of  the  stickleback 
adapted  to  their  functions  ?  The  tongue  in  most  fishes  is  wanting  or  very 
slightly  developed. 

Gill  Rakers.  —  If  we  open  wide  the  mouth  of  any  large  fish  and  look  in- 
ward, we  find  that  the  mouth  cavity  leads  to  a  funnel-like  opening,  the 
gullet.  On  each  side  of  the  gullet  we  can  see  the  gill  arches,  guarded  on 
the  inner  side  by  a  series  of  sharp  pointed  structures,  the  gill  raker  a.  In 
some  fishes  in  which  the  teeth  are  not  well  developed,  there  seems  to  be  a 
greater  development  of  the  gill  rakers,  which  in  this  case  are  used  to  strain 
out  small  organisms  from  the  water  which  passes  over  the  gills.  Many 
fishes,  as  the  shad  and  menhaden,  make  such  use  of  the  gill  rakers. 

Digestive  System. — The  gullet  leads  directly  into  a  baglike  stomach. 
There  are  no  salivary  glands  in  the  fishes.  There  is,  however,  a  large  liver, 
which  appears  to  be  used  as  a  digestive  gland.  This  organ,  becau.se  of  the 
oil  it  contains,  is  of  considerable  economic  importance.  Many  fishes  have 
a  number  of  pocketlike  outgrowths  from  the  intestines.  These  structures, 
called  the  pyloric  cceca,  are  believed  to  secrete  a  digestive  fluid.  The  intestine 
ends  at  the  vent,  which  is  usually  located  on  the  ventral  side  of  the  fish, 
immediatel}''  in  front  of  the  anal  fin. 


Anatomy  of  the  carp  ;  6r,  branchiae,  or  gill  openings  ;  c,  heart  ;  /,  liver  ;  vn,  swimming 

bladder  ;  d,  intestine. 

Swim  Bladder.  —  An  organ  of  unusual  significance,  called  the  swim 
bladder,  is  connected  with  the  digestive  tract  in  front  of  the  stomach.  In 
young  fishes  of  many  species  this  connection  is  a  tube,  which  in  some  forms 

hunter's  BIOL. 18 


274 


ZOOLOGY 


persists  throughout  h*fe,  but  which  in  other  fish  becomes  closed,  a  thin, 
fibrous  cord  taking  its  place.  The  swim  bladder  aids  in  giving  the  fish  such 
a  volume  that  it  displaces  a  weight  of  water  about  equal  to  its  own  weight. 
The  walls  of  the  organ  are  richly  supplied  with  blood  vessels,  and  it  thus 
undoubtedly  serves  as  an  organ  for  taking  in  oxygen.  It  has  been  compared 
to  a  lung  of  the  higher  vertebrates. 

Circulation  of  the  Blood.  —  In  the  vertebrate  animals  the  blood  is  said  to 
circulate  in  the  body,  because  it  passes  through  a  more  or  less  closed  system 
of  tubes  in  its  course  around  the  body.  In  the  fishes  the  heart  is  a  two- 
chambered  muscular  organ,  a  thin-walled  auricle  leading 
into  a  thick-walled  muscular  ventricle.  The  blood  is 
pumped  from  the  heart  to  the  gills ;  there  it  loses  some  of 
its  carbon  dioxide ;  it  then  passes  on  to  other  parts  of  the 
body,  eventually  breaking  up  into  very  tiny  tubes  called 
capillaries.  From  the  capillaries  the  blood  returns,  in 
tubes  of  gradually  increasing  diameter,  toward  the  heart 
again.  During  its  course  some  of  the  blood  passes  through 
the  kidneys  and  is  there  relieved  of  part  of  its  nitrog- 
enous waste.       (See  Chap.  XXX.) 

Circulation  of  blood  in  the  body  of  the  fish  is  rather  slow. 
The  temperature  of  the  blood  being  nearly  that  of  the 
surrounding  media  in  which  the  fish  lives,  the  animal  has 
incorrectly  been  given  the  term  cold-blooded. 

Nervous  System.  —  As  in  all  vertebrate  animals,  the 
brain  and  spinal  cord  of  the  fish  are  inclosed  in  a  series 
of  bony  structures  called  vertebrae.  The  central  nervous 
system  consists  of  a  brain,  with  nerves  leading  to  the 
organs  of  sight,  taste,  smell,  the  ear,  and  to  such  parts  of 
the  body  as  possess  the  sense  of  touch ;  a  spinal  cord ;  and 
spinal  nerves.  Nerve  cells  located  near  the  outside  of  the 
body  send  in  messages  to  the  central  system,  which  are 
there  received  as  sensations.  Cells  of  the  central  nervous 
system  in  turn  send  out  messages  which  result  in  the 
movement  of  muscles. 

We  have  already  learned  something  of  the  senses  of  a 
fish.  That  of  hearing  is  poorly  developed,  the  ear  being 
largely  an  organ  of  balancing.  Along  each  side  of  almost  every  species  of 
fish  is  found  a  line,  which  consists  of  a  series  of  tiny  pits  each  connected  with 
its  neighbor.^  This  lateral  line,  as  it  is  called,  is  believed  to  have  to  do 
with  the  sense  of  touch. 

Skeleton.  —  In  the  vertebrates,  of  which  the  bonj''  fish  is  an  example, 
the  skeleton  is  under  the  skin  and  is  hence  called  an  endoskeleton.  It  con- 
sists of  a  bony  framework,  the  vertebral  column,  and  certain  attached 

1  This  line  is  plainly  visible  in  some  fishes  because  of  its  dark  color. 


Plan  of  circulation 
in  fishes;  a, auri- 
cle; b,  ventricle; 
c,  branchial 
artery;  e,  bran- 
chial  veins, 
bringing  blood 
from  the  gills,  d, 
and  uniting  in 
the  aorta,  /;  g, 
vena  cava,  re- 
turning blood 
to  heart. 


THE  FISHES  275 

bones,  the  ribs,  with  other  spiny  bones  to  which  the  unpaired  fins  are  attached. 
The  paired  fins  are  attached  to  the  spinal  column  by  two  collections  of  bones, 
known  respectively  as  the  pectoral  and  'pelvic  girdles.  The  bones  serve  in 
the  fish  for  the  attachment  of  powerful  muscles,  by  means  of  which  loco- 
motion is  accomplished. 

The  Egg-laying  Habits  of  the  Bony  Fishes.  —  The  stickleback 
has  the  rather  curious  habit  (for  a  fish)  of  nest  building.  The  nest 
is  attached  to  waterweeds  or  a  submerged  stick.  It  is  almost 
circular  in  outline,  and  in  the  case  of  the  common  stickleback  is 
about  two  inches  in  diameter.  A  hole  in  the  top  gives  access  to 
the  interior.  In  this  nest  the  female  deposits  her  eggs,  which  are 
then  guarded  by  the  male  until  the  young  hatch  out.  The  fresh- 
water sunfish  also  has  the  habit  of  nest  building,  its  nest  being 
scooped  out  in  the  sand  of  the  lake  or  river  bed. 

The  eggs  of  most  bony  fishes  are  laid  in  great  numbers  at  the 
time  of  spawning.  This  number  varies  from  a  few  thousand  in 
the  trout  to  many  hundreds  of  thousands  in  the  shad  and  several 
millions  in  the  cod.  The  time  of  egg  laying  is  usually  spring  or 
early  summer.  Usually  the  eggs  are  left  to  develop  by  themselves, 
sometimes  attached  to  some  submerged  object,  but  more  frequentty 
free  in  the  water.  They  are  exposed  to  many  dangers,  and  both 
eggs  and  developing  fish  are  eaten,  not  only  by  birds,  fish  of  other 
species,  and  other  water  inhabitants,  but  also  by  their  own  relatives 
and  even  parents.  Consequently  a  very  small  percentage  of  eggs 
ever  reach  maturity. 

The  Relation  of  the  Spawning  Habits  to  Economic  Importance  of 
Fish.  —  The  spawning  habits  of  fish  are  of  great  importance  to  us 
because  of  the  economic  value  of  fish  to  mankind,  not  only  directly 
as  a  food,  but  indirectly  as  food  for  other  animals  in  turn  valuable 
to  man.  Many  of  our  most  desirable  food  fishes,  notably  the 
salmon,  shad,  sturgeon,  and  smelt,  pass  up  rivers  from  the  ocean  to 
deposit  their  eggs.  The  salmon  is  said  to  travel  thousands  of 
miles,  swimming  against  strong  currents  much  of  the  way,  leap- 
ing rapids  and  falls,  in  order  to  deposit  her  eggs  in  suitable 
localities,  where  the  conditions  of  water  and  food  are  requisite, 
and  the  water  shallow  enough  to  allow  the  sun's  rays  to  warm 
the   water  suflSciently   to   cause   the  eggs   to   develop.      At  the 


276 


ZOOLOGY 


time  of  the  spawning  migration  the  salmon  are  taken  in  vast 
numbers.  The  salmon  fisheries  net  over  $13,000,000  annually, 
the  shad  at  least  $1,500,000,  the  smelt  fishery  nearly  $150,000 
more.  The  total  annual  value  of  the  fisheries  of  the  United  States 
is  over  $50,000,000.  But  the  profits  from  these  fisheries  are  steadily 
decreasing  because  of  the  yearly  destruction  of  untold  millions  of 
eggs  which  might  develop  into  adult  fish.  State  and  government 
interposition  is  in  many  cases  coming  too  late,  for  at  the  present 
rate  of  destruction   many  of  our  most  desirable  food  fishes  will 


Fisheries — Percentage  Product 


JiL 


20 


JL 


^ 


IL 


J°.- 


ii° 


8.0 


m 


JL 


United  States     Gt.Brit.  &  Ir. 


Can.  & 
Newf. 


Japan 


Russia  France  ^'•^•, 


Rest  of  World 


soon  be  extinct.  The  sturgeon,  the  eggs  of  which  are  used  in  the 
manufacture  of  the  delicacy  known  as  caviare,  is  an  example  of  a 
fish  that  is  almost  extinct  in  this  part  of  the  world. 

Other  deep-water  fish  do  not  go  up  rivers  to  spawn,  but  lay  their 
eggs  in  the  sea.  In  such  eggs  there  is  found  a  tiny  oil  drop,  which, 
being  lighter  than  water,  causes  the  egg  to  come  to  the  surface  of 
the  water,  where  the  heat  of  the  sun  may  favorably  influence 
development.  Other  fish  change  their  habitat  at  different  times 
during  the  year,  moving  in  vast  schools  northward  in  summer  and 
southward  in  the  winter.  In  a  general  way  such  migrations  follow 
the  coast  lines.     Examples  of  such  migratory  fish  are  the  cod, 


THE  FISHES 


277 


menhaden,  herring,  and  bluefish.  The  migrations  are  due 
to  temperature  changes,  to  the  seeking  after  food,  and  to  the 
spawning  instinct.  Some  fish  migrate  to  shallower  water  in  the 
summer  and  to  deeper  water  in  the  winter;  here  the  reason  for 
the  migration  is  doubtless  the  change  in  temperature. 

The  herring  fisheries  have  always  been  a  source  of  wealth  to 
the  inhabitants  of  northern  Europe.  The  banks  and  shallows  of 
the  coast  of  Newfoundland  were  undoubtedly  known  to  the 
Norsemen  long  before  the  discovery  of  this  country  by  Columbus. 

Classification  of  Fishes.  —  The  animals  we  recognize  as  fishes  are 
grouped  by  naturalists  into  four  groups : 


Sand  shark,  an  elasmobranch.    Note  the  slits  leading  from  the  gills.    From  photograph 
loaned  by  the  American  Museum  of  Natural  History. 

1.  The  Elasmobranchs.  —  These  fishes  have  a  skeleton  formed  of  carti- 
lage which  has  not  become  hardened  with  lime.  The  gills  communicate  with 
the  surface  of  the  body  by  separate  openings  instead  of  having  an  operculum. 
The  skin  is  rough  and  the  eggs  few  in  number.  In  some  members  of  this 
group  the  young  are  born  alive.   Sharks,  rays,  and  skates  are  Elasmobranchs. 


Sturgeon  (Acipenser  sturio),  a  ganoid  fish. 

2.   Ganoids.  —  Fish  in  which  the  body  is  protected  by  a  series  of  plate- 
like scales  of  considerable  strength.     These  fishes  are  the  only  remnant  of 


278 


ZOOLOGY 


what  once  was  the  most  powerful  group  of  animals  on  the  earth,  the  great 
armored  fishes  of  the  Devonian  age.     The  gar  pike  is  an  example. 

3.  The  Teleosts  OR  Bony  Fishes. 
— They  compose  ninety-five  per  cent 
of  all  living  fishes.  In  this  group  the 
skeleton  is  bony,  the  gills  are  pro- 
tected by  an  operculum,  and  the  eggs 
are  numerous.  Most  of  our  common 
food  fishes  belong  to  this  class. 

4.  The  Dipnoi  or  Lung  Fishes. 
—  This  is  a  very  small  group,  in  many 

respects  more  like  amphibians  than  fishes,  the  swim  bladder  being  used 
as  a  lung.  They  live  in  tropical  Africa,  South  America,  and  Australia, 
inhabiting  the  rivers  and  lakes  there.  They  withstand  drying  up  in  the 
mud  during  the  dry  season,  lying  dormant  for  long  periods  of  time  in  a 
ball  of  mud  and  waking  to  active  life  again  when  the  mud  coat  is  removed 
by  immersion  in  water. 


A  bony  fish. 


Reference  Books 


FOR   THE    PUPIL 


Davison,  Practical  Zoology,  pages  185-199.     American  Book  Company. 
Herrick,  Text-Book  in  General  Zoology,  Chap.  XIX.     American  Book  Company. 
Nature  Study  Leaflets,  XIII.     N.Y.  Department  of  Agriculture. 
Hiinter  and  Valentine,  Laboratory  Manual  of  Zoology,  page  167.     Henry  Holt  and 

Company. 
Jordan,  Kellogg,  and  Heatli,  Animal  Studies,  XIV.     D.  Appleton  and  Company. 


FOR    THE    TEACHER 


Jordan  and  Evermann,  American  Food  and  Game  Fishes.     Doubleday,  Page,  and 

Company. 
Kingsley,  Text-book  of  Vertebrate  Zoology.     Henry  Holt  and  Company. 
Riverside  Natural  History.     Houghton,  Mifflin,  and  Company. 


XXIII.     AMPHIBIANS 

The  Frog;^  Body.  —  In  the  body  of  man  we  find  two  distinct  regions,  the 
head  and  trunk.  Are  such  regions  to  be  found  in  the  frog  ?  How  is  the 
shape  of  the  body  fitted  for  Hfe  in  the  water? 

Habitat.  —  There  is  considerable  difference  in  the  habitat  of  the  green 
frog  and  the  leopard  frog.  The  former  may  usually  be  found  in  ponds  or 
brooks  in  which  considerable  vegetation  is  found.  The  latter  live  in  pools 
or  woody  swamps  in  which  the  bottoms  are  dark  from  a  background  of 
dead  leaves  or  mud.  Remembering  this,  how  might  the  color  of  the  frog 
harmonize  with  its  surroundings?  Is  this  of  advantage  to  the  frog?  In 
what  respects? 

Protective  Resemblance.  —  Notice  the  position  of  the  frog  at  rest  in  the 
water.  In  its  natural  habitat  a  frog  in  this  position  would  scarcely  be 
noticed,  so  perfect  is  the  resemblance  to  the  surroundings.  Notice  that 
the  only  parts  of  the  frog  that  show  above  the  surface  of  the  water  are  the 
eyes  and  that  part  of  the  head  bearing  the  nostril  holes. 

Appendages.  —  Compare  the  anterior  limb  with  j^our  own  arm.  Identify 
in  each,  upper  arm,  forearm,  and  hand.  Note  the  number  of  fingers.  In 
the  same  manner  find  the  thigh,  shank,  and  foot  in  the  posterior  limb.  In 
what  respects  do  ankle  and  foot  differ  in  the  frog  and  in  man?  What 
adaptations  for  locomotion  (swimming)  do  you  find  in  the  frog  ? 

Skin.  —  Notice  the  slimy  skin  of  the  frog.  This  is  due  to  the  presence 
in  the  skin  of  cells  which  secrete  and  pour  out  mucus.  Might  this  slime 
be  of  any  use  to  the  animal  ?  The  skin  of  the  frog  is  supplied  with  numer- 
ous tiny  blood  vessels.  The  blood  in  these  thin-walled  tubes  gains  oxygen 
from  the  surrounding  atmosphere  and  from  the  water,  while  carbon  dioxide 
is  given  off.     Thus  the  skin  is  used  in  the  process  of  respiration. 

The  Eye.  — The  eye  of  the  frog  differs  somewhat  in  shape  from  our  own. 
Note  the  positions  on  the  side  of  the  head.  Touch  the  eye.  How  is  it 
protected  ?  Look  for  a  delicate  fold,  the  nictitating  membrane  (sometimes 
called  the  third  eyelid),  which  may  be  drawn  over  the  eye. 

Have  you  any  experience  as  to  the  keenness  of  vision  in  the  frog  ?  Do 
they  jump  into  the  water  because  they  see  or  hear  you  ?  Any  experiment 
which  will  throw  light  on  this  point  will  make  an  interesting  piece  of  original 
work  for  extra  credit.  Can  you  perform  any  experiment  which  will  show 
whether  the  frog  prefers  light  to  darkness  ? 

Ear.  — The  tympanic  membrane  or  eardrum  of  the  frog  may  be  found  on  the 
side  of  the  head.  It  is  a  circular  area  of  tightly  stretched  skin.  In  man  the 
ear  drum  is  beneath  the  surface  of  the  body  near  the  inner  end  of  the  canal 
or  tube  which  we  see  in  the  external  ear.  In  the  frog  and  in  man  a  connec- 
tion exists  between  the  mouth  and  the  inner  surface  of  the  ear  drum.  This 
tube  is  known  as  the  Eustachian  tube. 

Home  Experiment.  —  Give  an  account  of  any  experiment  that  you  may 
perform  that  will  prove  that  frogs  can  hear,  or  the  nature  of  sounds  that 
attract  their  attention. 

1  For  laboratory  exercise  see  Hunter  and  Valentine,  Manual,  page  170.  (Either 
the  green  frog  or  the  leopard  frog  may  beiised  for  the  laboratory  suggestions  given 
in  this  book.) 

279 


280 


ZOOLOGY 


Mouth.  —  Note  the  shape,  position,  and  relatively  large  size  of  the  mouth 
in  the  frog  as  compared  with  man. 

Make  a  drawing  of  the  frog  in  a  natural  position,  having  all  parts  visible 
in  the  drawing  carefully  labeled. 

Characteristics  of  Amphibia. —  The  frog  belongs  to  the  class  of  ver- 
tebrates known  as  the  Amphibia.  As  the  name  indicates,  members 
of  this  group  pass  more  or  less  of  their  life  in  the  water,  although  in 
the  adult  state  they  are  provided  with  lungs.     In  the  earlier  stages 

of  their  development  they 
take  ox3^gen  into  the  blood 
by  means  of  gills.  At  all 
times,  but  especially  during 
the  w^inter,  the  skin  serves 
as  a  breathing  organ.  The 
skin  is  soft  and  unprotected 
by  bony  plates  or  scales. 
The  heart  has  three  cham- 
bers, namely,  two  auricles 
and  one  ventricle.  Most 
amphibians  undergo  a  com- 
plete metamorphosis. 
Life  Habits  of  Green  Frog.  —  The  green  frog  inhabits  shallow 
fresh-water  ponds,  streams,  and  marshes.  Much  of  the  daytime 
they  may  be  seen  sunning  themselves.  They  live  to  a  large  extent 
upon  insects,  which  they  catch  by  protruding  their  long  bi-cleft 
tongue.  They  also  eat  small  algse  and  aquatic  animals,  and  are 
in  fact  omnivorous,  even  eating  their  own  young. 

Life  History.  —  During  the  first  warm  days  in  March  or  April,  look  for 
gelatinous  masses  of  frog's  eggs  attached  to  sticks  or  waterweed  in  shallow 
ponds.  Collect  some  and  try  to  hatch  them  out  in  a  shallow  dish  in  the 
window  at  home.  Make  experiments  to  learn  whether  temperature  aff'ects 
the  development  of  the  egg  in  any  way.  Place  eggs  in  dishes  of  water  in  a 
warm  room  and  in  a  cold  room,  also  some  in  the  ice  box.  Make  observa- 
tions for  several  weeks  as  to  rate  of  development  of  each  lot  of  eggs.  Also 
try  placing  a  large  number  of  eggs  in  one  dish,  thus  cutting  down  the  supply 
of  available  oxygen,  and  in  another  dish  near  by  under  the  same  conditions 
of  light  and  heat  place  a  few  eggs.  Do  both  batches  of  eggs  develop  with 
the  same  rapidity?  In  all  these  experiments  be  sure  to  use  eggs  from  the 
same  egg  mass,  so  as  to  insure  all  being  of  the  same  age. 

Development.  —  The  eggs  of  the  frog  are  laid  in  shallow  water  in 
the  early  spring.     Masses  of  several  hundred  are  deposited  at  a 


Full-grown  green  frog,  about  half  natural  size. 
Photographed  by  Overton. 


AMPHIBIANS 


281 


single  laying.  Immediately  before  leaving  the  body  of  the  female 
they  receive  a  coating  of  jellylike  material,  which  swells  up  after 
the  eggs  are  laid.  Thus  they  are  protected  from  the  attack  of  fish 
or  other  animals  which  might  use  them  as  food.  The  fertilized 
egg  soon  segments  (divides  into  many  cells) ,  and  in  a  few  days,  if  the 
weather  is  warm,  these  cells  have  grown  into  an  oblong  body  which 
shows  the  form  of  a  tadpole.  Shortly  after  the  tadpole  wriggles  out 
of  the  jellylike  case  and  begins  life  outside  the  egg.  At  first  it 
remains  attached  to  some  waterweed  by  means  of  a  suckerlike 
projection;  later  a  mouth  is  formed  at  this  point  and  the  tadpole 
begins  to  feed  upon  algae  or  other  tiny  water  plants.  At  this 
time  gills  are  present  on  the  outside  of  the  body.  Soon  after  this, 
the  external  gills  are  re- 
placed by  gills  which  grow 
out  under  a  fold  of  the  skin 
which  forms  an  operculum 
somewhat  as  in  the  fish. 
Water  reaches  the  gills 
through  the  mouth  and 
passes  out  through  a  hole  on 
the  left  side  of  the  body. 
As  the  tadpole  grows  larger, 
legs  appear,  the  hind  legs 
making  their  appearance 
first,  although  for  a  long  time 
locomotion  is  performed  by 
means  of  the  tail.  In  some 
species  of  frogs  the  changes 
from  the  egg  to  adult  are 
completed  in  one  summer. 
A  month  or  two  after  hatching,  the  tadpole  begins  to  eat  less, 
the  tail  is  used  up  rather  rapidly  (being  absorbed  into  other  parts 
of  the  body),  and  before  long  the  transformation  from  the  tad- 
pole to  the  young  frog  is  complete.  In  the  green  frog  and  bull- 
frog the  metamorphosis  is  not  completed  until  the  beginning  of 
the  second  summer.  The  large  tadpoles  of  such  forms  bur>'  them 
selves  in  the  soft  mud  of  the  pond  bottom  during  the  winter. 


Frog's  eggs  from  three  to  ten  hours  old.  All 
stages  from  four  cells  to  thirty-two  cells  may 
be  noted.  From  photograph,  enlarged  four 
times,  by  Davison. 


282 


ZOOLOGY 


Early  during  its  transformation  the  tadpole  loses  its  gills,  these 
being  replaced  by  lungs.  At  this  time  the  young  animal  may  be 
seen  coming  to  the  surface  of  the  water  after  a  bubble  of  air. 
Changes  in  the  diet  of  the  animal  also  take  place  at  this  stage  of 
metamorphosis;    the  long  coiled  intestine  is  transformed  into  a 


Stages  in  the  life  of  tadpoles  of  the  green  frog.    The  two  large  tadpoles  are  in  their  second 

summer.    Photographed  by  Overton. 


much  shorter  one  in  the  adult.  The  animal,  now  insectivorous  in 
its  diet,  becomes  provided  with  tiny  teeth  and  a  mobile  tongue, 
instead  of  keeping  the  horny  jaws  used  in  scraping  off  alga3.  After 
the  tail  has  been  completely  absorbed  and  the  legs  have  become 
full  grown,  there  is  no  further  structural  change  and  the  metamor- 
phosis is  said  to  be  complete. 


AMPHIBIANS  283 

The  Common  Toad.  —  One  of  the  nearest  of  the  allies  of  the 
frog  is  the  common  toad.  The  eggs,  like  those  of  the  frog,  are 
deposited  in  fresh-water  ponds,  especially  small  pools.  The  egg- 
laying  season  is  later  than  that  of  the  frog.  The  eggs  are  laid  in 
strings,  as  many  as  eleven  thousand  eggs  having  been  laid  by  a 
single  toad. 

Field  Work.  —  The  egg-laying  season  in  New  York  state  is  early  May. 
At  this  time  procure  a  female  that  has  not  laid  her  eggs  and  phice  her  in  aii 
aquarium.  If  undisturbed,  she  may  lay  her  eggs  in  captivity.  Compare 
the  bulk  of  the  eggs  after  they  are  laid  with  the  size  of  the  toad  that  laid 
them.  This  apparent  discrepancy  is  caused  by  the  swelling  of  the  gelati- 
nous substance  around  them.  If  possible,  count  the  number  of  eggs  laid 
by  one  female.^ 

Toad  tadpoles  may  be  distinguished  from  those  of  the  frog,  as 
they  are  darker  in  color,  and  have  a  more  slender  tail  and  a  rela- 
tively larger  body  than  those  of  the  frog.  The  metamorphosis 
occupies  only  about  two  months  at  the  temperature  of  New  York. 
During  the  warm  weather  the  tail  is  absorbed  with  wonderful 
rapidity,  and  the  change  from  a  tadpole  with  no  legs  to  that  of 
the  small  toad  living  on  land  is  often  accomplished  in  a  few  hours. 
This  has  given  rise  to  the  story  that  it  has  rained  toads  in  a  given 
locality,  because  during  the  night  thousands  of  young  toads  have 
changed  habitat  from  the  water  to  the  land. 

The  toad  is  of  great  economic  importance  to  man  because  of  its 
diet.  No  less  than  eighty-three  species  of  insects,  mostly  injurious, 
have  been  proved  to  enter  into  the  dietary.^  A  toad  has  been  ob- 
served to  snap  up  one  hundred  and  twenty-eight  flies  in  half  an 
hour.  Thus  at  a  low  estimate  it  could  easily  destroy  one  hundred 
insects  during  a  day  and  do  an  immense  service  to  the  garden 
during  the  summer.  It  has  been  estimated  by  Kirkland  that  a 
single  toad  may,  on  account  of  the  cutworms  which  it  kills,  be 
worth  $19.88  each  season  it  lives.  Toads  also  feed  upon  slugs 
and  other  garden  pests. 

Other  Amphibians.  —  The  tree  frogs  (called  tree  toads)  are 
familiar  to  us  in  the  early  spring  as  the  peepers  of  the  swamps. 
They  are  among  the  earliest  of  the  frogs  to  lay  their  eggs.     During 

*  See  Hodge,  Nature  Study  and  Life.  ,    ,      .         ■        m     j\ 

2  (See  Kirkland,  Habits,  Food  and  Economic  Importance  of  the  American  1  oad.) 
Bul.  46,  Hatch  Experiment  Station,  Amlierst,  Mass. 


284 


ZOOLOGY 


adult  life  they  spend  most  of  their  time  on  the  trunks  of  trees, 
where  they  receive  immunity  from  attack  because  of  their  color 
markings.  The  feet  of  the  tree  toad  are  modified  for  climbing  by 
having  little  disks  on  the  ends  of  the  toes,  by  means  of  which  it  is 

able  to  cling  to  verti- 
cal surfaces. 

Another  amphibian 
is  the  salamander,  a 
smooth-skinned,  four- 
limbed  animal,  often 
incorrectly  called  a 
lizard.  These  animals 
pass  their  early  life  in 
the  water,  later  com- 
ing out  on  land.  After 
passing  through  the  stages  of  the  segmenting  egg,  with  few  excep- 
tions they  breathe  by  means  of  external  gills;  later  they  may 
develop  lungs.  A  few  never  have  lungs,  but  breathe  through  the 
moist  skin. 


Spotted  salamander.      From  photograph  loaned  by  the 
American  Museum  of  Natural  History. 


Newt.    From  photograph  loaned  by  the  American  Museum  of  Natural  History. 

Still  other  amphibians  are  the  mud  puppies,  sirens  or  mud  eels, 
and  the  axolotl.  All  of  the  above  animals  differ  from  the  reptiles 
in  having  a  smooth  skin  with  no  scales,  and  in  passing  the  early 
stage  of  their  existence  in  the  water. 


AMPHIBIANS  285 


Classification  of  Amphibia  mentioned 

Order  I.    Urodela.     Amphibia    having    usually    poorly    developed    appendages. 

Tail  persistent  through  life.     Examples,  mud  puppy,  newt,  salamander. 
Order  II.    Anura.     Tailless     amphibia,     which     undergo     a     inotamorjjhosis  — 

breathe  by  gills  in  larval,  by  lungs  in  adult,  state.     Examples,  toad  and  frog. 


Reference  Books 
for  the  pupil 

Davison,  Practical  Zoology,  pages  199-211.     American  Book  Company. 
Herrick,  Text-book  in  General   Zoology,  Chap.  XX.       American   Book  Company. 
Nature  Study  Leaflets,  XVI,  XVII.     N.Y.  Department  of  Agriculture. 
Hunter  and  Valentine,  Laboratory  Manual  of  Biology,  pages  170-177.     Henry  Holt 

and  Company. 
Jordan,  Kellogg,  and  Heath.     Animal  Studies.     D.  Appleton  and  Company. 

for  the  teacher 

Holmes,  The  Biology  of  the  Frog.     The  Macmillan  Company. 

Parker  and  Haswell,  Text-book  of  Zoology.     The  Macmillan  Company. 


XXIV.     REPTILES 

The  Spotted  or  Mud  Turtle  (Chelopus  guttatus) .  —  For  a  classroom  exercise 
use  living  turtles.  The  body  is  flattened,  and  is  covered  on  the  dorsal  and 
ventral  sides  by  a  bony  framework.  This  covering  is  composed  of  plates 
cemented  to  the  true  bone  underneath,  the  whole  forming  one  horny  cover. 
What  is  the  general  arrangement  of  these  plates  ?  The  dorsal  covering  is 
known  as  the  carapace,  the  ventral  one  the  plastron,  the  connection  between 
them  the  bridge.  Allow  the  animal  to  remain  quiet  for  a  moment,  then 
touch  the  head  suddenly.  What  is  one  function  of  the  shell?  In  the  box 
turtle  this  adaptation  is  made  more  evident  by  a  hinge  in  the  plastron 
which  fits  over  the  head  and  legs  after  they  are  withdrawn  into  the  shell. 

Adaptations.  —  Place  a  lively  turtle  on  its  back.  How  does  it  attempt 
to  regain  equilibrium  ?  Notice  the  long  neck.  The  long  neck  and  powerful 
horny  jaws  are  of  great  use  to  the  animal  in  food  getting.  Allow  the 
turtle  to  crawl  on  the  table.  Then  place  it  in  a  dish  of  water.  How  are 
the  legs  adapted  to  movement  in  the  water  ?  How  is  the  foot  adapted  for 
other  purposes  ? 

Turtles  are  very  strong  for  their  size.  The  stout  legs  carry  the  animal 
slowly  on  land,  and  in  the  water,  being  slightly  webbed,  they  are  of  service 
in  swimming.  The  strong  claws  are  used  for  digging  especially  at  egg-lay- 
ing season,  for  some  forms  of  turtles  dig  large  holes  in  sandy  beaches  in 
which  the  eggs  are  deposited. 

Watch  a  turtle  feeding.  Notice  that  the  claws  are  used.  How?  The 
absence  of  teeth  makes  it  necessary  for  the  turtle  to  tear  the  food  with 

the  aid  of  the  strong  claws. 

The  sense  of  hearing  in  the  turtles  is  not  keen. 
The  tympanic  membrane  can  be  seen  just  behind 
the  eyes  on  the  sides  of  the  head.  Can  you  deter- 
mine by  experiment  anything  regarding  keenness 
of  vision  in  the  turtle  ?  Is  the  turtle  protectively 
colored?  Describe  any  evidences  you  may  see. 
Notice  that  the  yellow,  ventral  side  would  har- 
monize the  general  coloring,  looking  through  the 
water  toward  the  surface  of  the  pond.  The  yellow 
dots  on  the  black  background  look  in  the  water 
much  like  small  stones  or  sand  grains. 

Draw  the  turtle,  natural  size,  from  the  dorsal 
Western  painted  turtle.         side  and  label  all  the  parts  you  know. 

The  Turtles.  —  The  turtles  form  a  large  and  interesting  group 
of  animals.  They  are  mostly  aquatic  in  habit.  Some  exceptions 
are  found,  however,  as  in  the  case  of  the  box  tortoise  {Cistudo 
Carolina)  and  the  giant  tortoise  of  the  Galapagos  Islands.  This 
latter  animal  attains  a  weight  of  three  hundred  pounds  or  more 
and  may  be  over  four  feet  in  length  and  almost  three  feet  in 

286 


REPTILES 


287 


Box  tortoise  (Terrapin).    From  photograph  loaned 
by  the  American  Museum  of  Natural  History. 


thickness.  Many  of  the  sea-water  turtles  are  of  large  size,  the 
leatherback  and  the  green  turtle  often  weighing  six  hundred  to 
seven  hundred  pounds  each.  The  flesh  of  the  green  turtle  and 
especially  the  diamond- 
back  terrapin,  an  animal 
found  in  the  salt  marshes* 
along  our  southeastern 
coast,  are  highly  esteemed 
as  food.  Unfortunately 
for  the  preservation  of  the 
species,  these  animals  are 
usually  taken  during  the 
breeding  season,  when 
they  go  to  sandy  beaches 
to  lay  their  eggs. 

Characteristics  of  the  Reptilia.  —  The  turtle  belongs  to  the  class 
of  vertebrates  known  as  the  Reptilia.  These  animals  are  charac- 
terized by  having  scales  developed  from  the  skin.  These  in  the 
turtle  have  become  bony  and  are  connected  with  the  internal 
skeleton.  Turtles  always  breathe  by  means  of  lungs,  differing  in 
this  respect  from  the  amphibians.  They  seem  to  show  their  dis- 
tant relationship  to  birds  in  that  their  eggs  are  large  and  are 
encased  in  a  leathery,  limy  shell. 

Lizards.  —  Lizards  may  be  recognized  by  the  long  body  with 
four  legs  of  nearly  equal  size.  The  body  is  covered  with  scales. 
The  animal  never  lives  in  water,  it  is  active  in  habit,  and  it  does  not 
undergo  a  metamorphosis.  Salamanders  (commonly  called  lizards) 
have  a  moist  skin,  and  belong  to  the  Amphibia.  Lizards  are  harm- 
less creatures,  the  Gila  monster  of  New  Mexico  and  Arizona,  a 
poisonous  variety,  being  the  one  exception.  Lizards  are,  on  the 
whole,  of  economic  importance  to  man  because  they  eat  insects 
and  include  the  injurious  ones  in  their  dietary.  Certain  lizards, 
including  injurious  ones,  notably  the  chameleon  and  our  common 
fence  lizard,  have  the  power  to  change  the  color  of  the  skm. 
This  forms  a  protective  adaptation,  for  they  thus  assume  the 
color  of  their  immediate  surroundings.  The  horned  toad  of  our 
Western  states  shows  another  wonderful  case  of  protective  adap- 


288 


ZOOLOGY 


Horned  toad.     Note  the  protective  resemblance. 


tation.  The  iguana  of  Central  America  and  South  America  is 
among  the  largest  of  lizards,  growing  to  a  length  of  three  feet  or 
more.  It  has  the  distinction  of  being  one  of  the  few  edible  lizards. 
Snakes.  —  Probably  the  most  disliked  and  feared  of  all  animals 
are  the  snakes.     This  feeling,  however,  is  rarely  deserved.     Our 

common  snakes  are  harm- 
less and  were  it  not  for 
the  fact  that  they  live 
upon  insect  -  destroying 
animals,  as  toads,  frogs, 
and  birds,  we  might  even 
say  that  they  are  useful 
to  man. 

Snakes  are  almost  the 
only  legless  vertebrates. 
Although  the  limbs  are 
absent,  still  the  pelvic  and 
pectoral  girdles  are  de- 
veloped. The  Yevy  long 
backbone  is  made  up  of  a 
large  number  of  vertebrae, 
as  many  as  four  hundred 
being  found  m  the  boa  constrictor.  Ribs  are  attached  to  all  ver- 
tebrae in  the  region  of  the  body  cavity. 


Rattlesnake  three  feet  long  coiled  ready  to  strike. 
In  this  position  it  can  dart  its  head  forward  two 
feet  only.    From  photograph  by  Davison. 


REPTILES 


289 


Locomotion.  —  Locomotion  is  performed  by  pulling  and  push- 
ing the  body  along  the  ground,  a  leverage  being  obtained  by 
means  of  the  broad  flat  scales,  or  scutes,  with  which  the  ventral 
side  of  the  body  is  covered.  Snakes  can  also  move  without  twist- 
ing the  body.  This  is  accomplished  by  a  regular  drawing  forward 
of  the  scutes  (with  the  ribs  under  them)  and  then  pushing  them 
backward  rather  more  violently. 

Feeding  Habits.  —  The  bones  of  the  jaw  are  very  loosely  joined 
together.     Thus  the  mouth  of  the  snake  is  capable  of  wide  disten- 
tion.    It  holds  its  prey  by  means  of  incurved  teeth,  two  of  which 
(in  the  poisonous  snakes)  are  hollow,  and  serve  as  a  duct  for  the 
passage  of   poison.     The 
poison  glands  are  found 
at  the  base  of  the  curved' 
fangs  in  the  upper  jaw. 
The  tongue  is  very  long 
and  cleft  at  the  end.     It 
is  an  organ  of  touch  and 
taste,  and  is  not,  as  many 
people    believe,    used    to 
sting  with.     The  food  is 
swallowed     whole,    after 
having    been    caught   by 
the    teeth,    and    pushed 
down  by  rhythmic  contractions  of  the  muscles  surrounding  the 
gullet.     They  refuse  other  than  living  prey.     After  a  full  meal, 
one  of  which  is  sufficient  for  weeks,  the  snake  remains  in  a  torpid 
condition. 

Adaptations.  —  The  extreme  length  of  the  body  in  the  snake 
has  resulted  in  the  modification  of  the  form  of  its  internal  organs. 
One  long,  narrow  lung  is  developed  instead  of  two.  The  glands  of 
the  body  cavity  are  long  and  slender,  while  the  kidneys  are  placed 
so  that  one  is  anterior  to  the  other. 

Snakes  are  usually  colored  to  harmonize  with  their  surround- 
ings. Thus  they  may  approach  and  seize  their  prey  before  it 
escapes.  They  are  not  extremely  prolific  animals,  but  hold  their 
own  with  other  forms  of  life,  because  of  their  numerous  adaptations 

hunter's    BIOL.  —  19 


Skull  of  boa  constrictor,  two  thirds  natural  size. 
From  photograph  by  Davison. 


290 


ZOOLOGY 


for  protection,  their  noiseless  movement,  protective  color,  and,  in 
some  cases,  by  their  odor  and  poison. 

Poisonous  Snakes.  —  Not  all  snakes  can  be  said  to  be  harmless. 
The  bite  of  the  rattlesnake  of  our  own  country,  although  dangerous, 
seldom  kills.  The  dreaded  cobra  of  India  has  a  record  of  over  two 
hundred  and  fifty  thousand  persons  killed  in  the  last  thirty-five 
years.  The  Indian  government  yearly  pays  out  large  sums  for 
the  extermination  of  venomous  snakes,  over  two  hundred  thou- 
sand of  which  have  been  killed  during  a  single  year. 

Alligators  and  Crocodiles.  —  The  latter  are  mostly  confined  to 
Asia  and  Africa,  while  the  former  are  natives  of  this  continent  and 


Young  alligator.     One  fourth  natural  size. 

South  America.  The  chief  structural  difference  between  them  is 
that  the  teeth  in  alligators  are  set  in  long  sockets,  while  those  of 
the  crocodile  are  not.  Both  of  these  great  lizardlike  animals  have 
broad,  flattened  tails  adapted  to  swimmmg.  The  eyes  and  nostril 
holes  protrude  from  the  head,  so  that  the  animal  may  float  motion- 
less near  the  surface  of  the  water  with  only  eyes  and  nostrils 
visible.  The  nostrils  are  closed  by  a  valve  when  the  animal  is 
under  water.  They  feed  on  fishes,  but  are  known  to  attack  large 
animals,  as  horses,  cows,  and  even  man.  They  seek  their  prey 
chiefly  at  night ;  and  spend  the  day  basking  in  the  sun.  The  croc- 
odiles of  the  Ganges  River  in  India  levy  a  yearly  tribute  of  many 
hundred  lives  from  the  natives. 


REPTILES  291 


Classification  of  Reptiles 

Order  I.  Chelonia  (turtles  and  tortoises).  Flattened  reptiles  with  body  en- 
closed in  bony  case.  No  teeth  or  sternum  (breast  bone).  Examples,  snapping 
turtle,  box  tortoise. 

Order  II.  Lacertilia  (lizards).  Body  covered  with  scales,  usually  having  two- 
paired  appendages.      Breathe  by  lungs.     Example,  fence  lizard,  horned  toad. 

Order  III.  Ophidia  (snakes).  Body  elongated,  covered  with  scales.  No  limbs 
present.     Examples,  garter  snake,  rattlesnake. 

Order  IV.    Crocodilia.     Freshwater  reptiles  with  elongated  body  and  bony  scales 


on  skin.     Two  paired  limbs.     Examples,  alligator,  crocodile.  i 

Reference  Books 
for  the  pupil 

Davison,  Practical  Zoology,  pages  211-226.     American  Book  Company. 
Herrick,  Text-hook  in  General  Zoology,  Chap.  XXI.     American  Book  Company. 
Jordan,    Kellogg,   and   Heath,  Animal  Studies,   Chap.  XVI.      D.  Appleton  and 
Company. 

FOR    THE    TEACHER 

Riverside  Natural  History.     Houghton,  Mifflin,  and  Company. 

Parker  and  Haswell,  Text-book  of  Zoology.     The  Macmillan  Company. 


XXy.     BIRDS 


The  following  questions  may  be  worked  out  during  a  visit  to  a  zoological 
park  or  during  a  field  trip.^ 

Pick  out  some  particular  bird  for  your  study  and  take  notes  upon  the  fol- 
lowing series  of  questions.  Do  not  expect  to  be  able  to  answer  all  the  ques- 
tions which  follow. 

Protection.  —  Does  the  bird  rest  or  nest  in  trees,  bushes,  or  grass?  In 
general,  what  are  the  colors  of  the  bird?  Do  they  harmonize  with  the  sur- 
roundings when  the  bird  is  at  rest  ?  Look  especially  for  birds  on  the  nest. 
Often  such  birds  will  remain  quiet,  allowing  the  observer  almost  to  touch 

them  before  they  attempt  to  fly  away.  In 
some  cases  the  light,  glinting  through  the 
trees,  gives  a  mottled  or  banded  appearance 
to  the  leaves,  somewhat  resembling  the  same 
kind  of  markings  on  a  bird. 

Flight.  —  Watch  a  bird  in  flight.  Try 
to  determine  the  exact  changes  in  the  posi- 
tion of  the  wings  that  take  place.  The  tip 
of  the  wing  usually  describes  a  curve  which 
results  in  the  forming  of  the  figure  go  .  Notice 
that  the  rate  of  movement  of  the  wing  dif- 
fers greatly  in  different  birds.  Birds  with 
long,  thin  wings,  as  the  hawks  and  gulls, 
move  the  wing  in  flight  with  much  less  ra- 
pidity than  those  with  short,  wide  wings,  as 
the  grouse  or  quail.  The  latter  birds  start 
with  much  less  apparent  effort  than  the  birds 
with  longer  wings;  they  are,  however,  less 
capable  of  sustained  flight. 

The  wing  of  a  bird  is  slightly  concave  on 
the  lower  surface  when  outstretched.  Thus 
on  the  downward  stroke  of  the  wing  more 
resistance  is  offered  to  the  air. 

Under  the  covering  of  feathers  the  parts 
of  the  wing  may  be  made  out  This  may 
easily  be  done  from  a  fowl  at  home,  or  dead 
sparrows  may  be  used  in  the  laboratory. 
Find  and  identify  the  parts  corresponding 
to  the  human  arm,  forearm,  and  hand.  The 
last  division  of  the  wing  is  homologous  to  our 


B 

I^^^hV.I'iSB'  ^I 

^It^HI^H^^^^^^I 

■wvir  ■ 

BRnH^^^^^l 

Kll 

^|H| 

m^mm^^L 

^h|^^H 

■^^■^^M^^H 

^IBili^^S^I 

^^Far^^^^H 

^^^^s      ^^^^^^1 

HaB 

IHJH 

|^|Hl 

^^S'                  >^l^l 

^HM>      \:S^^SK^^k 

^H^ 

3^^^  -««I^^^^^H 

a^BB   '"iM^^^^^H 

ai^HL  '^'"'^^^^^^1 

^^^Ii^mB 

^^^H 

Feathers  of  a  meadow  lark.  Which 
of  the  above  are  used  for  flight  ? 
Why  ?  From  photograph  loaned 
by  the  American  Museum  of 
Natural  History. 


^  Bird  activities  may  best  be  studied  out  of 
doors.  Any  city  park  offers  more  or  less  oppor- 
tunity for  such  study,  for  several  of  our  native 
birds  make  the  parks  their  home.  If  not  these, 
then  the  English  sparrow  can  be  found  anywhere 
in  the  East.  The  best  time  for  making  observa- 
tions is  early  in  the  morning,  especially  in  the 
Spring  season. 

292 


BIRDS  293 

hand  and  wrist,  the  third  and  fourth  fingors  are  absent  while  the  wrist  bones 
and  fingers  of  the  fowl  have  grown  together,  thus  giving  greater  strength 
and  support.     This  is  evidently  an  adaptation  for  fliglit. 

Feathers.  —  Few  people  realize  that  the  body  of  a  bird  is  not  com- 
pletely covered  with  feathers.  Look  for  featherless  areas  on  the  body  of 
the  bird  you  are  working  with.  Notice  that  feathers  are  of  several  shapes. 
Soft  down  feathers  cover  the  body,  serving  for  bodily  warmth.  In  the 
wings  we  find  quill  feathers;  these  are  adapted  for  service  in  flight.  Let  us 
examine  a  single  quill  feather  more  closely.  The  main  axis  of  the  feather, 
called  the  shaft,  is  hollow,  light,  and  strong.  Ywrnx  the  shaft,  lateral 
branches,  called  barbs,  are  given  off".  The  barbs  give  rise  to  still  smaller 
lateral  structures,  the  barbules,  the  latter  just  visible  to  the  naked  eye.  Each 
barbule  is  interlocked  with  its  neighbor  by  means  of  many  microscopic  hooks, 
the  barbicels.  If  you  attempt  to  pull  apart  the  barbs  of  a  feather,  you 
will  find  that  they  stick  together.  What  is  the  reason  for  this?  Slight 
this  arrangement  be  of  use  in  flight,  and  if  so,  how? 

Draw  a  quill  feather  and  show  all  the  parts  visible  to  the  naked  eye. 

Feathers.  —  Feathers  are  developed  from  the  under  layer  of 
the  skin.  At  first  they  appear  to  be  tiny,  pimplelike  projections. 
They  are  formed  in  almost  exactly  the  same  manner  as  are  the 
scales  of  a  fish  or  a  lizard.  The  first  feathers  developed  on  the 
body  are  evidently  for  protection  against  cold  and  wet.  In 
aquatic  birds  the  feathers  are  oiled  constantly,  and  thus  shed 
water.  The  feathers  of  most  male  birds  are  brightly  colored. 
This  seems  to  make  them  attractive  to  the  females  of  the  species; 
thus  the  male  may  win  its  mate. 

Perching.  —  The  habit  of  perching  is  an  interesting  one.  In 
many  perching  birds  the  tendons  of  the  leg  and  foot,  which  regu- 
late the  toes,  are  self  locking ;  thus  while  asleep  such  birds 
balance  themselves  perfectly.  A  certain  part  of  the  ear,  known 
as  the  semicircular  canals,  has  to  do  with  the  function  of  balanc- 
ing. In  the  flamingoes,  which  do  not  perch,  balancing  appears  to 
be  automatic  and  self-regulating;  thus  the  bird  is  able  to  go  to 
sleep  when  in  an  upright  position. 

Tail.  —  The  tail  is  sometimes  used  in  balancing;  its  chief  func- 
tion, however,  appears  to  be  that  of  a  rudder  during  flight.  Note 
that  the  tail  is  merely  a  small  protuberance  of  the  body,  the 
feathers  which  grow  there  give  it  the  shape.  In  many  birds,  under 
the  skin  of  the  tail  is  located  a  large  oil  gland,  whence  comes 
the  supply  of  oil  that  is  used  in  waterproofing  the  feathers. 

Adaptation  in  the  Lower  Limbs.  —  In  the  leg  identify  the  thigh,  the  shin, 
and  foot.     The  ankle  of  the  bu-d  is  extremely  long,  the  seven  bones  found 


294 


ZOOLOGY 


in  man  are  here  in  part  lost  and  partly  grown  together.  Scales  are  found 
on  the  ankle  and  foot;  in  very  early  life  they  resemble  feathers,  both  in 
appearance  and  manner  of  growth.  If  mounted  specimens  are  obtainable, 
notice  the  different  feet  in  different  birds.  Some  have  the  foot  adapted 
to  perching,  others  for  swimming,  others  wading,  etc.  Take  some  one  ex- 
ample and  attempt  to  explain  all  the  devices  which  serve  to  adapt  the  foot 
to  its  use.  Is  there  anything  in  the  life  of  the  bird  that  would  make  the 
correlation  of  the  adaptation  of  the  foot  for  scratching  and  perching  ?  Note 
the  method  of  walking  in  a  sparrow,  robin,  and  pigeon.  What  is  there 
about  the  position  or  structure  of  the  leg  that  adapts  it  for  walking  or  hop- 
ping?    In  the  ostrich  and  cassowary  the  wings  are  not   used  for  flight; 


Explain,  after  reading  the  paragraph  on  adaptation  in  the  lower  limbs,  how  each  of  the 
above  feet  are  fitted  to  do  their  work.  From  photograph  loaned  by  the  American 
Museum  of  Natural  History. 

here  the  lower  limbs  have  taken  up  the  function  of  rapid  motion.  Notice 
any  adaptations  for  aquatic  life  that  you  may  find,  and  explain  in  each  case 
how  the  part  described  is  fitted  for  the  work  to  be  done.  The  foot  of  the 
common  barnyard  duck,  for  example,  is  much  like  that  of  the  alligator. 

The  Skeleton. — The  whole  skeleton  combines  Hghtness,  flexi- 
bihty,  and  strength.  Many  of  the  bones  are  hollow  or  have  large 
spongy  cavities.  The  bones  of  the  head  and  neck  show  many 
and  varied  adaptations  to  the  life  that  the  bird  leads.  The 
vertebrae  which  form  the  framework  of  the  neck  are  strong  and 


BIRDS 


295 


yet  flexible.  They  vary  greatly  in  shape  and  also  in  number.  The 
swan,  seeking  its  food  under  water,  has  a  neck  containing  twenty- 
three  long  vertebrae;  the  English 
sparrow,  in  a  different  environ- 
ment, has  only  fourteen  short  ones. 
Some  bones,  notably  the  breast- 
bone, are  greatly  developed  in  fly- 
ing birds  for  the  attachment  of 
the  muscles  used  in  flight. 

Bill.  — The  form  of  the  bill 
shows  adaptation  to  a  wonderful 
degree. 


Skeleton  of  a  fowl ;  C,  clavicle ;  C.  V.,  cer- 
vical vertebrae;  K.,  keeled  sternum; 
P.G.,  pelvic  girdle;  Pc.G.,  pectoral 
girdle. 


Exercise  for  a  Trip  to  a  Museum  or 
Zoological  Park.  —  Note  a  number  of 
different-shaped  bills.  How  is  the  bill 
adapted  to  taking  the  food  for  the  bird  ? 
Seek  for  uses  in  each  case.  Remember 
that  a  bird  uses  its  bill  as  some  ani- 
mals use  claws  and  teeth.  Birds,  ex- 
cept the  parrot  and  some  of  the  birds 
of  prey,  rarely  use  the  claws  in  feeding. 
The  bills  vary  greatly  according  to  the 
habits  of  the  birds.  A  duck  has  a  flat 
bill  for  pushing  through  the  mud  and 
straining  out  the  food;  a  bird  of  prey 
has  a  curved  or  hooked  beak  for  tear- 
ing; the  woodpecker  has  a  sharp 
straight  bill  for  piercing  the  bark  of 
trees  in  search  of  the  insect  larvae  which 
are  hidden  underneath. 

Birds  never  have  teeth,  except  possibly  in  the  embryo  stage.  The  edge  of 
the  bill  may  be  toothlike,  as  in  some  fish-eating  ducks;  these,  however,  are 
not  true  teeth.  Frequently,  too,  the  tongue  has  sharp  tooth  like  edges 
which  serve  the  same  purpose  as  the  recurved  teeth  of  the  frog  or  snako. 
With  care  you  may  be  able  to  make  out  the  use  of  the  tongue  in  eating 
and  drinking  in  some  bird.  Report  in  class  the  result  of  your  observa- 
tions. 

Reason  for  High  Temperature  and  Rapid  Heart  Beat  in  Birds.  —  ]Make 
observations  on  a  bird  as  to  the  rapidity  of  the  movements  made  in  breath- 
ing (respiratory  movements).  Compare  them  with  your  own  as  to  rapidity. 
Compare  the  rate  of  heart  beat  in  your  own  body  and  that  of  a  bird  (a  live 
sparrow  or  canary).  To  take  your  own  pulse,  find  the  artery  in  your  wrist 
or  on  the  side  of  your  head  about  an  inch  above  the  midpoint,  on  a  line 
between  the  ear  and  eye.  The  heart  of  the  bird  may  easily  be  felt  by  hold- 
ing the  hand  against  its  breast.  If  now  the  temperature  of  the  body  of 
the  bird  be  taken  (by  holding  a  clinical  thermometer  under  the  wing),  and 
this  compared  with  that  of  your  own  body  taken  under  the  arm,  a  con- 
siderable difference  will  be  noticed. 


296 


ZOOLOGY 


Adaptations  in  the  bills  of  birds. 


The  rate  of  respiration,  of  heart  beat,  and  the  body  temperature 
are  all  higher  in  the  bird  than  in  man.  All  these  correlated  facts 
show  that,  because  of  the  increased  activity  of  the  bird,  there 
comes  a  necessity  for  a  greater  and  more  rapid  supply  of  oxygen, 
an  increased  blood  supply  to  carry  the  material  to  be  used  up  in 
the  release  of  energy,  and  a  means  of  rapid  excretion  of  the  wastes 
resulting  from  the  process  of  oxidation.  The  bird  may  be  com- 
pared to  a  high-pressure  steam  engine.  In  order  to  release  the 
energy  which  the  bird  uses  in  flight,  a  large  quantity  of  fuel  which 
will  oxidize  quickly  must  be  used.  Birds  are  large  eaters,  and  the 
digestive  tract  is  fitted  to  digest  the  food  quickty  and  to  release  the 
energy  when  needed,  by  having  a  large  crop  in  which  food  may  be 
stored  in  a  much  softened  condition.  As  soon  as  the  food  is  part 
of  the  blood  it  may  be  sent  rapidly  to  the  places  where  it  is  needed, 
by  means  of  the  large  four-chambered  heart  and  large  blood 
vessels. 

This  is  one  of  the  greatest  adaptations  to  the  active  life  led 
by  a  bird.  Man  breathes  from  twelve  to  fourteen  times  per 
minute.  Birds  breathe  from  twenty  to  sixty  times  a  minute. 
The  lungs  are  not  large,  but  the  bronchial  tubes  are  continued 


BIRDS 


297 


through  the  lungs  into  hollow  spaces  filled  with  air,  which   are 
found  between  the  organs  of  the  body. 

The  high  temperature  of  the  bird  is  a  direct  result  of  this  rapid 
oxidation  and  also  because  the  feathers  and  the  oily  skin  form  an 
insulation  which  does  not  readily  permit  of  the  escape  of  heat. 
This  fact  is  of  much  use  to  the  bird  in  its  flights  at  great  altitudes, 
where  the  temperature  is  often  very  low. 

The  Nervous  System  and  the  Senses. — The  central  nervous  system  is  well 
developed.  A  large  forebrain  is  found,  which,  according  to  a  series  of 
elaborate  experiments  with  pigeons,  is  found  to  have  to  do  with  the 
conscious  life  of  the  bird.  The  cerebellum  takes  care  of  the  acts  which  are 
purely  mechanical  and  are  concerned  with  the  living  (digestion,  absorption, 
beating  of  the  heart,  etc.)  of  the  bird. 

Sight  is  probably  the  best  developed  of  the  senses  of  a  bird.  The  keen- 
ness of  vision  of  a  hawk  is  proverbial.  It  has  been  noticed  that  in  a  bird 
which  hunts  its  prey  at  night,  the  eyes  look  toward  the  front  of  the  face. 
In  a  bird  which  is  hunted,  as  in  the  dove,  the  eyes  are  placed  at  the  side  of 
the  head.  In  the  case  of  the  woodcock,  which  feeds  at  night  in  the  marshes, 
and  which  is  in  constant  danger  from  attack  by  owls,  the  eyes  have  come  to 
lie  far  back  on  the  top  of  the  head.  Hearing  is  also  well  developed  in  most 
birds;  this  fact  may  be  demonstrated  with  any  canary. 

The  sense  of  smell  does  not  appear  to  be  well  developed  in  any  bird,  and 
is  especially  deficient  in  seed-eating  birds,  most  seeds  having  little  odor. 

Nesting  Habits.  —  Among  the  most  interesting  of  all  instincts 
shown  by  birds  are  the  habits  of  nest  building.  We  have  found 
that  some  invertebrates,  as  spiders  and  ants,  protect  the  eggs  when 
laid.  In  the  vertebrate 
group  some  fishes  (as  the 
sunfish  and  stickleback) 
make  nests  for  the  depo- 
sition of  the  eggs.  But 
most  fishes,  and  indeed 
other  vertebrates  lower 
than  the  birds,  leave  the 
eggs  to  be  hatched  by  the 
heat  of  the  sun.  Birds 
incubate  their  eggs,  that 
is.,  hatch  them  by  the 
heat  of  their  own  bodies. 


Nest  of  a  pho-be  under  tin-  b;irii  tl<>'>r. 


298 


ZOOLOGY 


Nest  of  the  chimney  swift. 


Hence  a  nest,  in  which  to  rest,  is  needed.  The  ostrich  is  an  excep- 
tion;  it  makes  no  nest  but  the  male  and  the  female  take  turns 
in  sitting  on  the  eggs.  Such  birds  as  are  immune  from  the  attack 
of  enemies,  either  because  of  their  isolation,,  or  their  protective 

coloration  (as  the  puffins,  gulls^ 
and  terns),  build  a  rough  nest 
among  the  rocks  or  on  the 
beach.  The  eggs,  especially 
those  of  the  tern,  are  marked 
and  colored  so  as  to  be  al- 
most indistinguishable  from 
the  rocks  or  sand  on  which 
they  rest.  Other  birds  have 
made  the  nest  a  home  and  a 
place  of  refuge  as  well  as  a 
place  to  hatch  the  eggs.  Such 
is  the  nest  of  the  woodpecker 
in  the  hollow  tree  and  the 
hanging  nest  of  the  oriole. 
Some  nests  which  might  be  easily  seen  because  of  their  location 
are  often  rendered  inconspicuous  by  the  builders;  for  example, 
the  lichen-covered  nest  of  the  humming  birds. 

Care  of  the  Young.  —  After  the  eggs  have  been  hatched  the 
young  in  most  cases  are  quite  dependent  upon  the  parents  for  food. 
Most  young  birds  are  prodigious  eaters ;  as  a  result  they  grow  very 
rapidly.  It  has  been  estimated  that  a  young  robin  eats  two  or 
three  times  its  own  weight  in  worms  every  day.  Many  other 
young  birds,  especially  kingbirds,  are  rapacious  insect  eaters.  In 
the  case  of  the  pigeons  and  some  other  birds,  food  is  swallowed  by 
the  mother,  partially  digested  in  the  crop,  and  then  regurgitated 
into  the  mouths  of  the  young  nestlings. 

Food  of  Birds.  —  The  food  of  birds  makes  them  of  the  greatest 
economic  importance  to  our  country.  This  is  because  of  the  rela- 
tion of  insects  to  agriculture.  A  large  part  of  the  diet  of  most  of 
our  native  birds  includes  insects  harmful  to  vegetation.  Investi- 
gations undertaken  by  the  U.S.  Department  of  Agriculture  (Divi- 
sion of  Biological  Survey)  show  that  a  surprisingly  large  number 


BIRDS 


299 


of  birds  once  believed  to  harm  crops  really  perform  a  service  to 
the  farmer  by  killing  injurious  insects.  Even  the  much  mali<,med 
crow  lives  to  a  large  extent  upon  insects.  During  the  entire  year, 
the  crow  eats  about  25  per  cent  insect  food  and  29  per  cent  grain! 
In  May,  when  the  grain  is  sprout- 
ing, the  crow  is  a  pest,  but  he 
makes  up  for  it  during  the  re- 
mainder of  the  summer  by  eat- 
ing harmful  insects.  The  robin, 
whose  presence  in  the  cherry  tree 
we  resent,  during  the  rest  of  the 
summer  does  untold  good  by  feed- 
ing upon  noxious  insects.  Birds, 
as  a  rule,  feed  upon  the  sub- 
stances which  are  most  abundant 
around  them  at  the  time.  The 
following  quotation  from  I.  P. 
Trimble,  A  Treatise  on  the  Insect 
Enemies  of  Fruit  and  Shade  Trees, 
bears  out  this  statement:  "On 
the  fifth  of  May,  1864,  .  .  .  seven 
different  birds  .  .  .  had  been 
feeding  freely  upon  small  beetles. 
.  .  .  There  was  a  great  flight  of 
beetles  that  day;  the  atmosphere  was  teeming  with  them.  A  few 
days  after,  the  air  was  filled  with  Ephemera  flies  and  the  same 
species  of  birds  were  then  feeding  upon  them."  ^ 

^  During  the  outbreak  of  Rocky  Mountain  locusts  in  Nebraska  in  1874-1877, 
Professor  Samuel  Aughey  saw  a  long-billed  marsli  wren  carry  tliirty  locusts  to  her 
young  in  an  hour.  At  this  rate,  for  seven  hours  a  day,  a  brood  would  consume  210 
locusts  per  day,  and  the  passerine  birds  of  the  eastern  half  of  \cbraska,  allowing 
only  twenty  broods  to  the  square  mile,  would  destroy  daily  1()2,771,0(M)  of  tin* 
pests.  The  average  locust  weighs  about  fifteen  grains,  and  is  capable  each  day  of 
consuming  its  own  weight  of  standing  forage  crops,  which  at  SIO  per  ton  would  be 
worth  $1,743.97.  This  case  may  serve  as  an  illustration  of  the  vast  good  that  is 
done  every  year  by  the  destruction  of  insect  pests  fed  to  nestling  birds.  And  it 
should  be  remembered  that  the  nesting  season  is  also  that  when  the  destruction  of 
injurious  insects  is  most  needed;  that  is,  at  the  period  of  greatest  agricultural 
activity  and  before  the  parasitic  insects  can  be  depended  on  to  reduce  the  pests. 
The  encouragement  of  birds  to  nest  on  the  farm  and  tiie  tliscourageinent  of  nest 
robbing  are  therefore  more  than  mere  matters  of  sentiment ;  they  return  an  actual 
cash  equivalent,  and  have  a  definite  bearing  on  the  success  or  failure  of  the  crops.  — 
Year  Book  of  the  Department  of  Agriculture. 


AMERICAN  CROW 


EN0LI8H  SPAmOW 


Food  of  some  common  birds. 


300  ZOOLOGY 

There  are  exceptions  to  the  above  general  rule,  as  is  seen  by  the 
fact  that  locust-catching  starlings  breed  in  large  numbers  in  local- 
ities where  locusts  have  deposited  their  eggs.  At  seasons  when 
the  number  of  locusts  hatched  are  few,  many  starlings  die  from 
lack  of  food. 

Not  only  do  birds  aid  man  in  his  battles  with  destructive  insects, 
but  seed-eating  birds  eat  the  seeds  of  weeds.  This  fact  alone  is 
sufficient  to  make  birds  of  vast  economic  importance. 

Not  all  birds  are  insect  feeders.  Some,  as  the  cormorants, 
ospreys,  gulls,  and  terns,  are  active  fishers.  Sea  birds  also  live 
upon  shellfish,  and  crustaceans  (as  small  crabs,  shrimps,  etc.); 
some  even  eat  organisms  of  a  lower  grade  of  life.  The  kea  parrot 
takes  its  meal  from  the  muscles  forming  the  backs  of  living  sheep, 
while  other  birds  of  prey  eat  living  mammals,  sometimes  of  con- 
siderable size. 

Extermination  of  our  Native  Birds.  —  Within  our  own  times  we 
have  witnessed  the  almost  total  extermination  of  some  species  of 
our  native  birds.  The  American  passenger  pigeon,  once  very 
abundant  in  the  middle  west,  is  now  practically  extinct.  Audu- 
bon, the  greatest  of  all  American  bird  lovers,  gives  a  graphic 
account  of  the  migration  of  a  flock  of  these  birds.  So  numerous 
were  they  that  when  the  flock  rose  in  the  air  the  sun  was  darkened, 
and  at  night  the  weight  of  the  roosting  birds  broke  down  large 
branches  of  the  trees  in  which  they  rested.  To-day  hardly  a  single 
specimen  of  this  pigeon  can  be  found.  Wholesale  killing  for 
plumage,  eggs,  and  food,  and  alas,  often  for  mere  sport,  has  caused 
the  decrease  of  our  common  song  birds  to  a  small  percentage  of  their 
former  number  within  the  past  fifteen  years.  Every  crusade 
against  indiscriminate  killing  of  our  native  birds  should  be  wel- 
comed by  all  thinking  Americans.  Without  the  birds  the  farmer 
would  have  a  hopeless  fight  against  insect  pests.  The  effect  of 
killing  native  birds  is  now  well  seen  in  Italy  and  Japan,  where 
insects  are  increasing  yearly  and  do  greater  damage  each  year  to 
crops  and  trees. 

Of  the  eight  hundred  or  more  species  of  birds  in  the  United 
States  only  two  species  of  hawks,  the  great  horned  owl,  the  cow- 
bird,  and  the  English  sparrow  may  be  considered  as  enemies  of  man. 


BIRDS  301 

The  English  Sparrow.  —  The  English  sparrow  is  an  example  of 
a  bird  introduced  for  the  purpose  of  insect  destruction,  that  has 
done  great  harm  because  of  its  relation  to  our  native  birds. 
Introduced  at  Brooklyn  in  1850  for  the  purpose  of  exterminating 
the  canker  worm,  it  soon  abandoned  an  insect  diet  and  has  driven 
out  most  of  our  native  insect  feeders.  Dirty  and  very  prolific,  it 
has  worked  its  way  from  the  East  as  far  as  the  Pacific  coast.  In 
this  area  the  bluebird,  song  sparrow,  and  yellowbird  have  all 
been  forced  to  give  way,  as  well  as  many  larger  birds  of  great 
economic  value  and  beauty.  The  English  sparrow  should  be 
exterminated. 

Geographical  Distribution  and  Migrations.  —  Most  of  us  are 
aware  that  some  birds  remain  with  us  in  a  given  region  during  the 
whole  year,  while  other  birds  appear  with  the  approach  of  spring, 
departing  southward  with  the  warm  weather  in  the  fall  of  the 
year.  Such  birds  we  call  migrants,  while  those  that  remain  the 
year  round  are  called  residents. 

In  Europe,  where  the  problem  of  bird  migration  has  been 
studied  carefully,  migrations  appear  to  take  place  along  well- 
defined  paths.  These  paths  usually  follow  the  coast  very  exactly, 
although  in  places  they  may  take  the  line  of  coast  that  existed  in 
former  geological  times.  This  seems  to  show  that  when  a  path 
has  been  established,  it  is  handed  down  from  one  generation  of 
birds  to  the  next  and  so  to  successive  generations. 

In  this  country  the  migration  routes  are  comparatively  un- 
known. It  has  been  found  that  the  Mississippi  Valley,  a  former 
arm  of  the  sea,  forms  one  line  of  migration,  while  the  north  Atlantic 
seacoast  is  another  route.  There  is  opportunity  for  a  careful 
observer  to  learn  much  of  the  spring  or  fall  migrations  in  the 
particular  part  of  the  country  in  which  he  resides.  All  information 
thus  obtained  should  be  sent  to  the  secretarv^  of  the  American 
Ornithologists'  Union  or  to  W.  W.  Cooke  of  the  Biological  Survey, 
who  has  done  much  to  establish  what  we  already  know  about  bird 
migration  in  this  country. 

It  has  been  recently  shown  by  the  Department  of  Agriculture 
that  the  southern  movement  of  migratory  birds  in  the  fall  of  the 
year  is  not  due  entirely  to  the  advent  of  cold  weather.      It  is 


302 


ZOOLOGY 


largely  a  matter  of  adjustment  to  food  supply.  A  migrant  almost 
always  depends  to  a  large  extent  upon  fruits,  seeds,  and  grains  as 
part  of  its  food.  Most  winter  residents,  as  the  crow,  are  omniv- 
orous in  diet.  Others,  as  the  sparrows,  may  be  seed  eaters,  but 
under  stress  may  change  their  diet  to  almost  anything  in  the  line 
of  food;  still  others,  as  the  woodpeckers,  although  insect-eating 
birds,  manage  to  find  the  desired  food  tucked  away  under  the 
bark  of  trees.  Most  insect-eating  birds,  however,  because  their 
food  is  found  on  green  plants,  are  forced  southward  by  the  cold 
weather.  Migrations  are  almost  entirely  due  to  need  of  food 
which  cannot  be  obtained  during  a  time  when  vegetation  is 
dormant  and  the  ground  is  frozen. 

Classification  of  Birds.  —  Birds  are  divided  into  two  great  groups,  de- 
pending on  the  development  of  the  keel,  that  is,  the  part  of  the  sternum  to 

which  the  muscles  used  in  flight 
are  attached.  This  bone  is  well 
known  to  every  one  who  has 
ever  picked  the  breastbone  of 
a  chicken.  Hence  all  flying 
birds  are  placed  in  a  group 
called  the  Carinatce. 

Birds  in  which  the  keel  of 
the  breastbone  is  not  well  de- 
veloped, such  as  the  ostrich  and 
cassowary,  are  said  to  belong  to 
the  Ratitce.  These  birds  make 
up  for  their  lack  of  wing  de- 
velopment by  having  the  legs 
strong  and  long. 

The  flying  birds  are  further 
subdivided  into  a  number  of 
orders,  the  classification  based 
upon  the  adaptations  of  differ- 
ent parts  of  the  bird,  especially 
the  legs  and  feet,  the  wings 
and  the  bill,  to  different  func- 
tions. We  shall  not  trouble 
ourselves  to  learn  all  the  differ- 
ent groups,  but  shall  content 
ourselves  with  picking  out  some  of  the  more  evident  and  important  ones. 
I.  Perching  Birds. — To  this  order  belong  most  of  our  common  birds. 


African  ostrich  {Struthio  camelvs). 


BIRDS 


303 


—  sparrows,  swallows,  larks,  blackbirds,  orioles,  kingbirds,  and  many  others 
well  known  to  every  bird  lover.  In  this  group  the  toes  are  so  placed,  three 
toes  being  turned  forward  and 
one  backward,  as  to  be  perfectly 
adapted  to  perching.  A  large 
number  of  our  sweetest  song- 
sters belong  among  the  perchers, 
the  warblers,  wrens,  thrushes, 
bluebirds,  and  last  but  not 
least,  our  robin. 

II.  The  Fowls  or  Gallina- 
ceous Birds. —  This  order  is  of 
great  economic  importance. 
From  the  jungle  fowl,  found 
wild  in  the  jungles  of  India,  all 
our  domesticated  fowls  have  de- 
scended. Other  familiar  exam- 
ples are  the  turkeys,  quails,  partridge  or  ruffed  grouse,  and  the  pheasants  and 
prairie  chickens.  In  this  group  the  legs  are  strong  and  stout,  the  body  thick- 
set, the  bill  and  claws  rather  blunt.  Birds  of  this  order  do  not  fly  far  in  a 
state  of  nature,  preferring  to  live  on  or  near  the  ground.  Such  birds  as  the 
ruffed  grouse,  which  nest  on  the  ground,  are  almost  invariably  protectively 


White-throated  sparrow  {Zonotrichia  albicuUis). 


Ptarmigan  in  winter.    Davison,  Zoology. 


colored     Another  interesting  example  of  protective   resemblance  in  this 
grouf  is  seen  in  the  ptarmigan.    This  bird  in  the  winter  is  white  as  the 


304 


ZOOLOGY 


Ptarmigan  in  summer.     Davison,  Zoology. 

are  best  known  to  us  are  the  hawks, 
the  condor,  with  its  great  sweep  of 
ten  feet  from  wing  to  wing,  and 
the  eagle.  To  the  hawks  belong 
two  birds  which  are,  because  of  their 
habits,  harmful  to  man.  They  are 
the  sharp-shinned  hawk  and  Coop- 
er's hawk. 

IV.  Waders. — These  are  birds 
with  unusually  long  legs  and  long 
necks,  the  latter  character  being  a 
natural  correlation  of  greatest  ser- 
vice in  food  getting.  Examples  are 
the  mud  hen  or  coot,  the  snipe, 
crane,  heron,  and  stork.  The  last 
two  are  the  giants  of  the  group. 

The  Swimmers  and  Divers. — • 
Birds  placed  in  these  orders  have 


snow  which  surrounds  it;  in 
the  spring  it  molts,  turning 
to  a  gray  and  white,  thus  re- 
sembling the  lichens  among 
which  it  feeds. 

III.  Birds  of  Prey. — 
These  birds  are  character- 
ized by  the  strong  hooked 
beak,  adapted  to  tearing,  and 
by  the  sharp  claws,  which  are 
curved  and  strong.  The  need 
of  a  gizzard,  which  is  a  promi- 
nent part  of  the  digestive 
tract  in  a  grain-eating  bird, 
has  here  almost  completely 
disappeared,  the  crop  serving 
to  macerate  the  food.  Owls 
show  this  use  of  the  muscu- 
lar gullet  and  crop,  for  the 
hair  and  skeletons  of  the  mice 
which  form  their  prey  are 
ejected  in  a  small  ball,  by 
means  of  this  muscular  organ. 
Members  of  this  group  that 


Golden  eagle  (Aquila  chrysactos).  North  Amer- 
ica and  Europe.  Copyright,  1901,  by  N.Y, 
Zoological  Society. 


BIRDS 


305 


,/:««».• 


Sandhill  crane,  showing  habitat.     From  mounted  group  at  the  American  Museum  of 

Natural  History. 


the  feet  webbed,  the  wings  are  often  adapted  for  long  and  swift  flight. 
In  this  division  are  placed  the  gulls,  terns,  ducks,  geese,  loons,  auks,  and 
puffins. 

Other  Orders.  —  Other  orders  of  birds  which  we  are  likely  to  see  and 
recognize  may  be  mentioned.  They  include  the  doves,  the  only  remaining 
native  representative  being  the  mourning  dove ;  the  woodpeckers,  strong  and 
long  of  bill,  the  friend  of  the  lumberman  as  a  savior  of  the  trees  from  boring 
pests  which  live  under  the  bark ;  the  swifts  and  humming  birds,  the  latter 
among  the  tiniest  of  all  vertebrate  animals:  and  the  parrots,  of  which  we 
have  only  one  native  form,  the  Carolina  paroquet  (Conurus  carolinensis) . 
This  bird  once  had  a  range  north  as  far  as  the  Great  Lakes;  now  it  is  found 
only  in  South  America. 

Relationship  of  Birds  and  Reptiles. — The  birds  afford  an  interesting 
example  of  how  the  history  of  past  ages  of  the  earth  has  given  us  a  clew  to 
the  structural  relation  which  birds  bear  to  other  animals.     Several  years 

hunter's    BIOL.  —  20 


306 


ZOOLOGY  ?. 

i. 


ago,  two  fossil  skeletons  were  found  in  Europe  of  a  birdlike  creature  which 
had  wings  and  feathers,  and  also  teeth  and  a  lizardlike  tail.  From  these 
fossil  remains  and   certain    structures    (as  scales)  and  habits  (as  the  egg- 


Common  tern  {Sterna  hirundo)  and  young,  showing  nesting  and  feeding  habits. 
From  group  at  American  Museum  of  Natural  History. 

laying  habits),  naturalists  have  concluded  that  birds  and  reptiles  in  distant 
times  were  nearly  related  and  that  our  existing  birds  probably  developed 
from  a  reptilelike  ancestor  millions  of  years  ago. 


Classification  of  Birds 

Division    I.    Ratitce.      Running  birds  with  no  keeled  breastbone.      Examples, 

ostrich,  cassowary. 
Division  II.    Carinatce.     Birds  with  keeled  breastbone. 

Order  i.    Passeres.     Perching  birds  ;  three  toes  in  front,  one  behind.     One  half 
of  the  birds  are  included  in  this  order.     Examples,  sparrow,  thrush,  swallow. 

Order  ii.    Gallince.      Strong    legs;     feet    adapted    to    perching.      Beak    stout. 
Examples,  jungle  fowl,  grouse,  quail,  domestic  fowl. 

Order  hi.    Raptores.     Birds  of  prey.     Hooked  beak.      Strong  claws.      Exam- 
ples, eagle,  hawk,  owl. 

Order  iv.    Grallatores.      Waders,      Long    neck,    beak,    and    legs.     Examples, 
snipe,  crane,  heron. 


BIRDS  307 

Order  v.  Natatores.  Divers  and  swimmers.  Legs  short,  toes  webbed. 
Examples,  gull,  duck,  albatross. 

Order  vi.  Columhoe.  Like  Gallinse  but  with  weaker  legs.  Examples,  dove, 
pigeon. 

Order  vii.  Picarioe.  Woodpeckers.  Two  toes  point  forward,  two  back- 
ward, and  adaptation  for  climbing.     Long,  strong  bill. 


Reference  Books 
for  the  pupil, 

Herrick,  Text-hook  in  General  Zoology,  Chaps.  XXII,  XXIII.     American  Bock 

Company. 
Beebe,  The  Bird.     Henry  Holt  and  Company. 
Nature  Study  Leaflets,  XXII,  XXIII,  XXIV,  XXV.    Cornell  University. 

FOR    THE    TEACHER 

Apgar,  Birds  of  the  United  States.     American  Book  Company, 

Beebe,  The  Bird.     Henry  Holt  and  Company. 

Bulletins  of  U.S.  Department  of  Agriculture,  Division  of  Biological  Survey,  Nos.  1, 

6,  15,  17.     See  also  Year  Book,  1899. 
Chapman,  Bird  Life.     D.  Appleton  and  Company. 
Riverside  Natural  History,  Vol.  IV.     Houghton,  Mifflin,  and  Company, 


XXVI.    MAMMALS 


Wood  hare.     From  photograph  loaned  by 
the  American  Museum  of  Natural  History. 


The  Rabbit.  ■ — •  Living  rabbits  may  be  kept  in  the  Schoolroom  in  a  box 
open  at  one  end,  the  open  end  protected  by  a  door  covered  with  wire  screen- 
ing. A  rabbit  thus  kept,  if  given  a  little  care,  soon  becomes  accustomed  to 
his  surroundings  and  will  prove  a  very  acceptable  addition  to  the  laboratory. 

Adaptations  to  Its  Life.  —  The  rab- 
bit in  a  wild  state  makes  its  home 
under  clumps  of  dried  grass,  brush,  and 
the  like.  Its  English  cousins  make 
burrows  in  the  ground.  The  rabbit 
escapes  observation  from  its  enemies 
by  means  of  its  color,  which  often 
closely  resembles  that  of  the  thickets 
in  which  it  hides.  Notice  the  body 
covering;  is  it  uniform  in  color  and 
thickness?  The  hair  forms  a  protec- 
tion from  the  cold.  In  summer  the 
color  of  the  coat  is  more  earthlike  than 
in  the  winter.  Some  arctic  forms  un- 
dergo a  complete  change  of  coat  from 
gray  in  summer  to  white  in  the  winter. 
Compare  the  fore  limbs  of  the  rab- 
bit with  your  own  arms;  do  you  find 
upper  arm,  forearm,  wrist,  and  hand? 
In  the  same  manner  find  the  parts 
corresponding  to  thigh,  shank,  and  foot  in  your  own  leg.  Notice  the  differ- 
ent methods  of  locomotion  in  the  rabbit;  seek  the  ways  in  which  the  limbs 
of  the  rabbit  are  adapted  to  the  function  of  locomotion.  Notice  the  feet 
to  see  if  they  are  adapted  for  digging  or  for  any  other  purpose. 

The  rabbit  relies  principally  on  swiftness  and  agility  in  flight  rather  than 
in  ability  to  cope  with  an  enemy  with  teeth  and  claws.  Frequently  they 
will  remain  in  absolute  quiet,  allowing  their  arch-enemy,  the  dog,  to  pass 
close  to  them,  relying  on  their  protective  coloration  to  escape  notice.  When 
chased  bj^  the  dog,  they  have  the  instinct  of  running  in  a  circle  and  will 
during  the  chase  suddenly  jump  to  one  side  at  a  sharp  angle  in  order  to 
throw  the  dog  off  the  scent. 

The  teeth  are  of  considerable  importance  in  connection  with  the  food 
and  the  method  of  obtaining  food.  Notice  the  prominent  cutting  teeth  (the 
incisors).  Note  the  cleft  upper  lip.  Feed  a  carrot  to  the  rabbit  and  deter- 
mine the  use  of  the  cleft.  Which  jaws  move  during  feeding  ?  Notice  that 
they  move  sidewise  as  well  as  vertically;  this  horizontal  movement  is  of 
considerable  use  in  grinding  the  food. 

If  you  examine  the  prepared  skull  of  a  rabbit  the  different  kinds  of 
teeth  may  be  easily  identified  and  their  functions  learned.  In  front  are 
found  the  incisors.  How  many  in  each  jaw?  Separated  from  the  inci- 
sors by  a  gap  are  the  molars  or  grinding  teeth.  How  are  such  teeth 
adapted  to  their  function?     With  a  hand  glass  note  the  position  of  the 

308 


MAMMALS 


309 


Skull  of  a  porcupine,  a  rodent.  Notice  the  large  overlap- 
ping incisor  teeth.  Compare  with  teeth  of  dog  (see 
page  313). 


molars  in  your  own 
mouth.  Do  you  find  teeth 
of  any  other  shape  than 
those  just  described? 

Compare  the  position 
and  shape  of  the  eye  with 
that  of  your  own.  Is  the 
eye  protected  in  any 
other  way  than  by  posi- 
tion ?  Note  the  bony  eye 
socket  in  the  skull,  the 
lids  (number),  and  any 
other  adaptations.  Touch 
the  eye  very  lightly  and 
see  the  third  or  "wink- 
ing" eyelid  (the  nictitat- 
ing membrane). 

Notice  the  shape  and  position  of  the  external  ear.  Compare  with  the 
head  in  length.  The  external  ear  collects  the  sound  waves  and  sends 
them  into  the  internal  ear,  the  true  organ  of  hearing  (see  page  421). 
Test  the  animal's  response  to  sounds,  especially  when  the  maker  of  the 
sound  is  hidden.  Is  the  hearing  of  the  rabbit  acute?  (The  above 
problem  makes  a  good  series  of  home  experiments.) 

Notice  the  mobility  of  the  nose,  especially  when  the  animal  is  sniffing. 
By  means  of  some  strongly  smelling  substances,  determine  whether  the 
rabbit  easily  perceives  odors.  Try  to  determine  whether  the  saying  that 
the  whiskers  of  a  cat  or  rabbit  are  used  to  smell  with  has  any  foundation 
in  fact.  Notice  whether  the  hairs  move  at  the  same  time  the  odor  is 
presented. 

Skeleton. — The  rabbit  is  provided  with  a  bony  skeleton  which  gives 
support  to  the  muscles  and  also  protects  the  delicate  organs  of  digestion,  res- 
piration, etc.,  under  the 
ribs.  Compare  with  the 
skeleton  of  man  in  this 
respect  (see  page  372), 
The  bones  of  the  skele- 
ton may  be  divided  into 
two  groups  as  in  man, 
—  those  of  the  axial 
skeleton,  the  vertebrae, 
and  bones  of  the  head; 
and  those  of  the  append- 
ages, including  the  pec- 
toral and  pelvic  arches, 
where  the  appendages 
are  attached  to  the  axial 


The  skeleton  of  a  monkey,  a  typical  mammal. 


skeleton.  Part  for  part  and  almost  bone  for  bone  the  skeleton  of  the  rabbit 
may  be  compared  with  that  of  man  (see  page  372) .  The  chief  differences 
exist  in  the  appendages,  where  the  erect  animal,  man,  has  the  bones  of  the 


310  ZOOLOGY 

hand  and  foot  considerably  modified  from  those  of  an  animal  which  uses 
all  the  appendages  for  locomotion.  The  digestive  tract  is  also  much  like 
that  of  man.     (See  page  330.) 

Organs  of  Digestion.  —  The  digestive  glands,  and  the  salivary,  gastric, 
intestinal,  and  pancreatic  glands  have  nearly  all  the  same  position  and 
functions.  The  glands  which  act  upon  starch  are  better  developed  in  the 
rabbit  than  in  man  because  of  the  predominance  of  starchy  foods  used  by 
the  rabbit.     The  intestine  is  longer  than  in  flesh-eating  animals. 

Circulation.  —  In  all  mammals  (of  which  the  rabbit  is  an  example)  the 
blood  in  its  circulation  passes  through  a  four-chambered  heart.  There  is  a 
system  of  closed  blood  tubes  which,  according  to  the  position  and  function, 
are  named  arteries,  veins,  and  capillaries.  The  whole  process  of  circulation 
is  identical  with  that  process  in  man  (see  Circulation,  page  350).  The 
lungs  and  heart  are  separated  from  the  lower  part  of  the  body  cavity  by 
means  of  a  thin -walled  plate  of  muscle,  called  the  diaphragm.  This  dia- 
phragm occurs  in  all  mammals. 

Oxygen  is  taken  up  by  the  blood  and  respiration  takes  place  in  a  similar 
manner  to  that  process  in  man. 

In  like  manner  the  organs  of  excretion  of  nitrogenous  waste,  the  skin  and 
kidneys,  eliminate  the  waste  from  the  body  in  the  same  manner  as  it  is  done 
in  man. 

Nervous  System.  —  The  brain  and  central  nervous  system  of  the  rabbit 
are  well  developed.  A  brain,  which  has  a  large  cerebrum  and  other  char- 
acteristics of  the  brain  of  man,  supplies  sense  organs  through  twelve  cranial 
(brain)  nerves  (see  The  Nervous  System,  page  400) .  The  senses,  especially 
those  of  sight  and  hearing,  are  also  highly  developed  and  are  very  acute. 
We  have  seen  that  the  eyes  are  so  placed  that  the  animal  is  able  to  look  to 
the  sides  and  behind  without  turning  the  head.  Organs  of  taste,  the  taste 
buds,  such  as  are  found  in  man,  are  also  developed  in  the  rabbit.     The  sense 

of  touch  appears  to  be  well  developed 
over  the  entire  body,  but  is  especially 
keen  in  the  region  of  the  nose  (see 
The  Senses,  page  419). 

Characters     of     Mammals.  — 
Vertebrate  animals  which  have  a 
The  common  house  rat.  From  photograph,     hairy  coat  and  which  nurse  the 

about  one  fourth  natural  size.  y^^^^^  ^^  ^^^^^   ^f  milk-produc- 

ing  glands  (the  mammary  glands)  are  called  mammals.  Such  evi- 
dently is  the  rabbit.  Rats,  woodchucks,  cattle,  dogs,  cats,  and 
man  are  all  examples  of  this  group.  Man  is  by  far  the  best  men- 
tally developed  of  all  this  group  and  is  therefore  spoken  of  as  the 
highest  of  the  mammals. 


MAMMALS 


311 


Rodents.  —  The  mammals  are  divided  into  a  number  of  smaller 
groups,  called  orders.  The  rabbit,  because  it  has  prominent 
incisor  teeth  and  no  canine  (dog)  teeth,  is  placed  in  the  order 
of  the  rodents.  Among  the  fourteen  orders  of  mammals  the 
rodents  are  estimated  to  comprise  fully  one  half  of  the  total 
number  of  species. 

Although  most  rodents  may  be  considered  as  pests  (as  the  rat 
and  mouse),  others  are  of  use  to  man.  Some  of  this  order  furnish 
food  to  man,  as  the  rabbit,  hares,  and  squirrels.  The  fur  of  the 
beaver,  one  of  the  largest  of  this  order,  is  of  considerable  value, 
as  are  the  coats  of  several  other  rodents.  The  fur  of  the  rabbit 
is  used  in  the  manufacture  of  felt  hats.  The  quills  of  the  por- 
cupines (greatly  developed  and  stiffened  hairs)  have  a  slight 
commercial  value. 

Other  Orders  of  Mammals. — The  lowest  are  the  monotremes,  ani- 
mals which  lay  eggs  hke  the  birds,  although  they  are  provided  with  hairy 
covering  like  other  mammals. 
Such  are  the  spiny  ant-eater  and 
the  duck  mole. 

All  other  mammals  bring 
forth  their  young  alive.  The 
kangaroos  and  opossum,  how- 
ever, are  provided  with  a  pouch 
on  the  ventral  side  of  the  body  in 
which  the  very  immature,  blind, 
and  helpless  young  are  nourished 
until  they  are  able  to  care  for 
themselves.  These  pouched  ani- 
mals are  called  marsupials. 

The  other  mammals,  in  which  the  young  are  born  able  to  care  for  them- 
selves, and  have  the  form  of  the  adult,  may  be  briefly  classified  as  follows : 


Virginia  opossum.    From  photograph,  one  eighth 
natural  size,  by  N.  F.  Davis. 


Character 
Edentates       Toothless    or    with    very    simple 

teeth 

Rodents  Incisor   teeth,  chisel-shaped,  usu- 

ally two  above  and  two  be- 
low 

Cetaceans        Adapted    to    marine    life,    teeth 

sometimes    platelike 


Examples 
Ant-eater 
Sloth 
Armadillo 
Beaver,  Rat 
Porcupine,  Rabbit 
Squirrels 
Whales 
Porpoise 


312 


ZOOLOGY 


Ungulates 


Carnivora 


Character 

Examples 

Hoofs,  teeth,  adapted  for  grinding; 

(a)  Odd-toed 

herb  eaters 

Horse 

Rhinoceros 

Tapir 

(b)  Even-toed 

Ox 

Pig 

Sheep 

Deer 

Long  canine  teeth,  sharp  and  long 

Dogs 

claws;  flesh  eaters 

Cats 

Lions 

Bears,  etc. 

Seals  and  Sea  lions 

Fore  limbs  adapted  to  flight,  teeth 

Bat 

pointed 

Erect     or     nearly     so,     fore     ap- 

Monkeys 

pendage  provided  with  hand 

Apes 

Man 

Chiroptera 


Primates 


Adaptations  in  Mammalia.  —  Mammals  are  considered  the 
highest  type  of  all  animals  for  reasons  that  have  already  been 
given.  Of  the  thirty-five  hundred  species,  most  inhabit  conti- 
nents; few  species  are  found  on  different  islands,  and  some,  as  the 
whale,  inhabit  the  ocean.  They  vary  in  size  from  the  whale  and 
the  elephant  to  tiny  shrew  mice  and  moles.  Adaptations  to 
different  habitat  and  methods  of  life  abound ;  the  seal  and  whale 
have  the  limbs  modified  into  fins,  the  sloth  and  squirrel  have 
limbs  peculiarly  adapted  to  climbing,  w^hile  the  bats  have  the  fore 
limbs  modeled  for  flight.  In  those  mammals  known  as  rodents, 
the  teeth  are  so  modified  that  on  the  upper  and  lower  jaw  two 
prominent  incisor  teeth  can  be  used  for  gnawing.  These  teeth 
keep  their  chisel-like  edge  because  the  back  part  of  the  teeth  is 
softer  and  wears  away  more  rapidl3^  The  beaver  fells  trees  with 
them.  We  are  all  familiar  with  the  destructive  gnawing  qualities 
of  one  of  the  commonest  of  all  rodents,  the  rat. 

Carnivorous  Mammals.  —  As  the  word  carnivorous  denotes, 
these  animals  are  to  a  large  extent  flesh  eaters.  In  a  wild  state 
they  hunt  their  prey,  which  is  caught  and  torn  with  the  aid  of 
well-developed  claws  and  long,  sharp  canine  teeth.     These  teeth, 


MAMMALS 


813 


Beaver  {Castor  canadensis).     North  America.    Copyright,  1900,  by  A.  RadcH£fe  Dugmore. 

SO  well  developed  in  the  dog,  are  known  as  the  dog  teeth.     All 

flesh-eating  mammals  are  wandering  hunters  in  a  state  of  nature; 

many,   as   the   bear  and 

lion,  have  homes  or  dens 

to    which    they    retreat. 

Some,  for  example  bears 

and  raccoons,  live  at  least 

part    of    the   time   upon 

berries  and  fruit.     Seals, 

sea  lions,  and  walruses  are 

adapted  to  a  life  in  the 

water.     Especially  in  the 

seals,  the  hind  limbs  are 

almost  useless  on  land.     Some  of  the  fur  bearers,  as  the  otter  and 

mink,  lead  a  partially  aquatic  life.      Others  in  this  great  group 

prefer  regions  of  comparative  dryness,  as  the  inhabitants  of  the 

South  African  belt.     Some  have  come  to  live  most  of  their  time 

in  the  trees,  the  raccoon  being  an  example.     Many  have  adapta- 


SkuU  of  a  dog.    Notice  the  size  and  shape  of  the 
canine  teeth. 


314  ZOOLOGY 

tions  for  food  getting  and  escape  from  enemies,  the  seasonal 
change  in  color  of  the  weasel  is  an  example  of  an  adaptation 
which  serves  both  of  the  above  purposes.  This  is  only  one  of 
hundreds  of  others  that  might  be  mentioned. 


The  California  sea  lion  {Zalophus  calif ornianus).    Photographed  in  the  Philadelphia 

Zoological  Gardens  by  Davison. 

Economic  Importance.  — The  Carnivora  as  a  group  are  of  much 
economic  importance  as  the  source  of  most  of  our  fur.  The  fur 
seal  fisheries  alone  amount  to  millions  of  dollars  annually.  Otters, 
skunks,  sables,  weasels,  and  minks  are  of  considerable  importance 
as  fur  products.  In  India  tigers  do  considerable  harm  in  some 
localities,  and  in  our  own  country  wolves,  pumas,  and  wild,  cats  do 
some  damage. 

Ungulates:  Hoofed  Mammals.  —  This  group  includes  the  domesti- 
cated animals  as  the  horse,  cow,  sheejD,  and  pig.  A  group  of  ani- 
mals which  originally  roamed  wild,  they  eventually  came  under 
the  subjugating  influence  of  man.  Now  they  form  a  source  of 
the  world's  wealth,  and  are  an  important  part  of  the  wealth 
of  the  United  States. 

The  order  of  ungulates  is  a  very  large  one.  It  is  characterized 
by  the  fact  that  the  nails  have  grown  down  to  become  thickened 
as  hoofs.  In  some  cases  only  two  (the  third  and  fourth)  toes 
are  largely  developed.  Such  animals  have  a  cleft  hoof,  as  in  the 
ox,  deer,  sheep,  and  pigs.     These  form  the  even-toed  ungulates. 


MAMMALS 


315 


Virginia  deer.    From  photograph  loaned  by  the 
American  Museum  of  Natural  History, 


Even-toed  Ungulates. 

—  The  deer  family  are 
the  largest  in  number  of 
species  and  individuals 
among  our  native  forms, 
and  in  fact  the  world  over. 
Among  them  are  the  com- 
mon Virginia  deer  of  the 
Eastern  states,  the  white- 
tailed  deer  of  our  Adiron- 
dack forests.  All  males 
of  the  deer  family  pos- 
sess horns  which  are  solid 
and  are  shed  annually. 
The  antelopes  and  giraffes 
have  also  solid  horns,  but 
do  not  shed  them.  The  bison,  or  buffalo,  is  nearly  related  to 
the  deer  and  wild  cattle.  Formerly  bisons  existed  in  enormous 
numbers  on  our  Western  plains.  They  were  hunted  by  whites 
and  Indians  for  the  hides  and  tongues   only,   and  thousands   of 

carcasses  were  left  to  rot 
after  a  hunt.  They  are  now 
almost  extinct. 

Odd-toed  Ungulates. — In 

some  ungulates  the  middle 

toe  of  the  foot  has  become 

largely  developed,  with  the 

result  that  the  animal  stands 

on  it.  Such  are  the  zebra  and 

the  horse,  andthe  rhinoceros, 

which  has  also  the  second 

and  fourth  toes  in  each  foot. 

—  We    have,    from    time  to 

that   certain   forms  of    life, 

the    earth    in    former    geo- 


The  buffSio  (bison).    'Photographed  by  the  New 
York  Zoological  Society. 


Geologic    History  of  the    Horse. 

time,    made   reference   to   the   fact 

now   almost   extinct,   flourished   on 

logic  periods.     One  type  of   animal   which   under  domestication 

has  become  greatly   improved   is   the   horse.     It   is    interesting 


316  ZOOLOGY 

to  note  that  America  was  the  original  home  of  the  horse.  Ages 
ago,  the  ancestor  of  the  present  horse  was  not  larger  than  a  fox 
terrier,  and  instead  of  having  one  toe  prolonged  into  a  hoof,  it 
walked  on  five  toes.  Later  changes  probably  caused  the  little 
horse  to  abandon  the  life  it  led  in  the  swamp  for  that  on  drier 
land.  At  that  time  it  v*^as  about  the  size  of  a  sheep  and  had 
three  toes  in  each  foot.  Later  the  longer-legged  and  single-toed 
horses  probably  became  speedier,  thus  escaping  from  the  numerous 
carnivores  which  must  have  preyed  upon  them.  So  ultimately 
by  very  gradual  variation  the  present  horse  was  evolved.  This 
purely  hypothetical  history  was  probably  repeated  with  variations 
in  the  case  of  many  other  species  of  animals. 

Man^s  Place  in  Nature.  —  Although  we  know  that  man  is  sepa- 
rated mentally  by  a  wide  gap  from  all  other  animals,  in  our  study 
of  physiology  we  must  ask  where  we  are  to  place  man.  If  we 
attempt  to  classify  man,  we  see  at  once  he  must  be  placed  with 
the  vertebrate  animals  because  of  his  possession  of  a  vertebral 
column.  Evidently  too,  he  is  a  mammal,  because  the  3^oung  are 
nourished  by  milk  secreted  by  the  mother  and  because  his  body 
has  at  least  a  partial  covering  of  hair.  Anatomically  we  find  that 
we  must  place  man  with  the  apelike  mammals,  because  of  these 
numerous  points  of  structural  likeness.  The  group  of  mammals 
which  includes  the  monkeys,  apes,  and  man  we  call  the  primates. 

Reference  Books 
for  the  pupil 

Davison,  Practical  Zoology,  pages  261-292.     American  Book  Company. 
Herrick,  Text-hook  in  General  Zoology,  Chap.  XXIV.     American  Book  Company 
Ingersoll,  Wild  Neighbors.     The  Macmillan  Company. 
Ingersoll,  Life  of  the  Mammals.     The  Macmillan  Company. 

FOR    THE    TEACHER 

Dodge,  General  Zoology,  pages  177-202.     American  Book  Company. 
Riverside  Natural  History.     Houghton,  Mifflin,  and  Company. 


PART  III.     HUMAN  PHYSIOLOGY 


XXVII.     FOODS 

Why  we  need  Food.  —  We  have  already  defined  food  as  anything 
that  forms  material  for  the  growth  or  repair  of  the  body  of  a  plant  or 
animal,  or  that  furnishes  energy  for  it.  Food,  then,  not  only  fur- 
nishes our  body  with  material  to  grow,  but  also  gives  us  the 
energy  we  expend  in  the  acts  of  walking,  running,  breathing, 
and  even  in  thinking. 

Nutrients. — Certain  nutrient  materials  form  the  basis  of  food  of 
both  plants  and  animals.  These  have  been  stated  to  be  carbohy- 
drates (starches,  sugars,  gums,  etc.),  hydrocarbons  (fats  and  oils, 
both  animal  and  vegetable),  proteids  (such  as  lean  meat,  eggs,  the 
gluten  of  bread),  and  mineral  matter  and  water.  Oxygen,  although 
not  a  nutrient,  ought  to  be  considered  as  food  because  it  enters 
into  the  composition  of  the  body,  and  without  it  no  energ}^  could 
be  released.  Let  us  apply  this  general  knowledge  with  reference 
to  the  human  body  in  order  to  determine  the  uses  made  of  food 
taken  into  the  body;  for  parts  of  the  human  body,  be  they  muscle, 
blood,  nerve,  bone,  or  gristle,  are  built  up  from  the  nutrients  in  our 
food. 

The  Body  a  Machine. — The  body  has  been  likened  to  a  machine 
in  that  it  turns  over  the  latent  or  potential  energy  stored  up  in 
food  into  kinetic  energy  (mechanical  work  and  heat)  which  is 
manifested  when  we  perform  work.  One  great  difference  exists 
between  an  engine  and  the  human  body.  The  engine  uses  fuel 
unlike  the  substance  out  of  which  it  is  made.  The  human  bodv, 
on  the  other  hand,  uses  for  fuel  the  same  substances  out  of  which 
it  is  formed;  it  may,  indeed,  use  part  of  its  own  substance  for  food. 

Let  us  now  consider  more  in  detail  the  nutrients  used  by  man 
as  food,  and  determine  the  use  of  each  to  him. 

Proteids.  —  As  we  know,  proteids,  in  some  manner  unknown 
to  us,  are  manufactured  in  the  leaves  of  plants.     Proteid  sub- 

317 


318  HUMAN   PHYSIOLOGY 

stances  contain  the  element  nitrogen.  Hence  such  foods  are 
called  nitrogenous  foods.  Although  about  four  fifths  of  the  at- 
mosphere is  composed  of  nitrogen,  yet  plants  are  unable  to  take 
it  from  the  air,  but  are  forced  to  absorb  it  through  the  roots  in  the 
form  of  nitrates  dissolved  in  the  water  in  the  soil.  Herbivorous 
animals  eat  the  plants,  take  into  their  bodies  the  stored  nitroge- 
nous foods,  and  change  this  food  into  protoplasm.  Man  himself 
must  form  the  protoplasm  of  his  body  (that  is,  the  muscles,  ten- 
dons, nervous  system,  blood  corpuscles,  the  living  parts  of  the  bone 
and  the  skin,  etc.)  from  nitrogenous  food.  Some  of  this  he  obtains 
by  eating  the  flesh  of  animals,  and  some  he  obtains  directly  from 
plants  (for  example,  peas  and  beans).  Because  of  their  chemical 
composition,  proteids  are  considered  to  be  flesh-forming  foods. 
They  are,  however,  oxidized  to  release  energy  if  occasion  requires  it. 

Organic  Fats  and  Oils.  —  Fats  and  oils,  both  animal  and  vegetable, 
are  the  materials  from  which  the  body  derives  much  of  its  energy. 
The  chemical  formula  of  a  fat  shows  that,  compared  with  other 
food  substances,  there  is  very  little  oxygen  present ;  hence  the 
greater  capacity  of  this  substance  for  uniting  with  oxygen. 
The  rapid  burning  of  fat  compared  with  the  slower  combustion 
of  a  piece  of  meat  or  a  piece  of  bread  illustrates  this.  A  pound 
of  butter  releases  over  twice  as  much  energy  to  the  body  as  does 
a  pound  of  sugar  or  a  pound  of  steak.  Human  fatty  tissue  is 
formed  in  part  from  fat  eaten,  but  carbohydrates  and  even  pro- 
teids may  be  changed  and  stored  in  the  body  as  fat.  The  Arctic- 
living  tribes  exist  almost  entirely  on  the  blubber  of  the  walrus  or 
the  whale.  The  blubber  not  oxidized  in  the  body  is  stored  as  fat, 
thus  forming  an  insulation  under  the  skin,  which  aids  in  keeping 
the  body  warm. 

Carbohydrates.  —  We  see  that  the  carbohydrates,  like  the  fats, 
contain  carbon,  hydrogen,  and  oxygen.  Here,  however,  the 
oxygen  and  hydrogen  are  united  in  the  molecule  in  the  same 
proportion  as  are  hydrogen  and  oxygen  in  water.  Carbohydrates 
are  essentially  energy -producing  foods.  They  are,  however,  be- 
lieved to  be  of  some  use  in  building  up  or  repairing  tissue.  Some 
experiments  seem  to  indicate  that  carbohydrates  may  be  formed 
directly  into  tissue.     It  is  certainly  true  that  in  both  plants  and 


FOODS  319 

animals,  such  foods  pass  directly,  together  with  foods  containing 
nitrogen,  to  repair  waste  in  tissues,  thus  giving  the  needed  propor- 
tion of  carbon,  oxygen,  and  hydrogen  which  is  to  unite  with  the 
nitrogen  in  forming  the  protoplasm  of  the  body. 

Inorganic  Foods. — Water  forms  a  large  part  of  almost  every 
food  substance.  The  human  body,  by  weight,  is  composed  of 
about  sixty  per  cent  water.  When  we  drink  water,  we  take 
with  it  most  of  the  inorganic  salts  used  by  the  body  in  the 
making  of  bone  and  in  the  formation  of  protoplasm.  Sodium 
chloride  (table  salt),  an  important  part  of  the  blood,  is  taken  in 
as  a  flavoring  upon  our  meats  and  vegetables.  So  important  is 
this  food  that  life  is  often  given  in  exchange  for  it  by  herbivorous 
animals,  as  the  deer.  Man  will  also  endure  great  hardships  to  get 
salt.^  Phosphates  of  lime  and  potash  taken  in  water  are  im- 
portant factors  in  the  formation  of  bone. 

Uses  of  Nutrients. — The  following  table  sums  up  the  uses  of 
nutrients  to  man :  ^ 


All  serve  as  fuel 
and  yield  energy  in 
form  of  heat  and 
muscular  strength. 


Proteid Forms    tissue     (mus-- 

White  (albumen)  of  eggs,  curd         cles,  tendon,  and 
(casein)   of  milk,  lean  meat,         probably  fat), 
gluten  of  wheat,  etc. 

Fats Form  fatty  tissue. 

Fat  of  meat,  butter,  olive  oil, 
oils  of  corn  and  wheat,  etc. 

Carbohydrates Transformed  into  fat. 

Sugar,  starch,  etc. 

Mineral  matters  (ash) Aid  in  forming  bone. 

Phosphates  of  lime,  potash,  assist  in  digestion,  etc. 

soda,  etc, 

^  Animals  will  travel  long  distances  to  obtain  salt.  Men  will  barter  gold  for  it ; 
indeed,  among  the  Gallas  and  on  the  coast  of  Sierra  Leone,  brothers  will  sell  their 
sisters,  husbands  their  wives,  and  parents  their  children  for  salt.  In  the  district 
of  Accra,  on  the  gold  coast  of  Africa,  a  handful  of  salt  is  the  most  valuable  thing 
upon  earth  after  gold,  and  will  purchase  a  slave  or  two.  Mungo  Park  tells  us  that 
with  the  Mandingoes  and  Bambaras  tiie  use  of  salt  is  such  a  luxury  that  to  say  of  a 
man,  'he  flavors  his  food  with  salt,'  is  to  imply  that  he  is  rich;  and  children  will 
suck  a  piece  of  rock  salt  as  if  it  were  sugar.  No  stronger  mark  of  respect  or  affec- 
tion can  be  shown  in  Muscovy  than  the  sending  of  salt  from  the  tables  of  the  rich 
to  their  poorer  friends.  In  the  book  of  Leviticus  it  is  expressly  commanded  as  one 
of  the  ordinances  of  Moses,  that  every  oblation  of  meat  upon  the  altar  shall  be 
seasoned  with  salt,  without  lacking ;  and  hence.it  is  called  the  Salt  of  the  Covenant 
of  God.  The  Greeks  and  Romans  also  used  salt  in  their  sacrificial  cakes ;  and 
it  is  still  used  in  the  services  of  the  Latin  church  —  the  ' parva  mica,'  or  pinch  of 
salt,  being,  in  the  ceremony  of  baptism,  put  into  the  child's  mouth,  while  the  priest 
says,  'Receive  the  salt  of  wisdom,  and  may  it  be  a  propitiation  to  thee  for  eternal 
life.'  —  Letheby,  On  Food. 

2  W.  O.  Atwater,  Principles  of  Nutrition  and  Nutritive  Value  of  Food.  U.S. 
Dept.  of  Agriculture,  1902. 


320  HUMAN   PHYSIOLOGY 

How  THE  Nutritive  Value  of  Food  has  been  Discovered.  —  For  a 
number  of  years,  experiments  have  been  in  progress  in  different  parts  of 
the  civilized  world  which  have  led  to  the  beliefs  regarding  food  that  have  just 
been  quoted.  One  of  the  most  accurate  and  important  series  of  experi- 
ments was  made  a  few  years  ago  by  the  late  Professor  W.  O.  Atwater  of 
Wesleyan  University,  in  cooperation  with  the  United  States  Department  of 
Agriculture.  By  means  of  a  machine  called  the  respiration  calorimeter 
(Lat.  caZor=  heat +  mefrwm= measure)  which  measures  both  the  products  of 
respiration  and  the  heat  given  off  by  the  body,  it  has  been  possible  to  deter- 
mine accurately  the  value  of  different  kinds  of  food,  both  as  fuel  and  as 
tissue  builders.  This  respiration  calorimeter  is  described  by  Professoi 
Atwater  as  follows :  — • 

"  Its  main  feature  is  a  copper-walled  chamber  7  feet  long,  4  feet  wide,  and 
6  feet  4  inches  high.  This  is  fitted  with  devices  for  maintaining  and  measur- 
ing a  ventilating  current  of  air,  for  sampling  and  analyzing  this  air,  for 
removing  and  measuring  the  heat  given  off  within  the  chamber,  and  for 
passing  food  and  other  articles  in  and  out.  It  is  furnished  with  a  folding 
bed,  chair,  and  table,  with  scales  and  appliances  for  muscular  work,  and 
has  telephone  connection  with  the  outside.  Here  the  subject  stays  for  a 
period  of  from  three  to  twelve  days,  during  which  time,  careful  analyses 
and  measurements  are  made  of  all  material  which  enters  the  body  in  the 
food,  and  of  that  which  leaA^es  it  in  the  breath  and  excreta.  Record  is 
also  kept  of  the  energy  given  off  from  the  body  as  heat  and  muscular  work. 
The  difference  between  the  material  taken  into  and  that  given  off  from  the 
body  is  called  the  balance  of  matter,  and  shows  whether  the  body  is  gain- 
ing or  losing  material.  The  difference  between  the  energy  of  the  food  taken 
and  that  of  the  excreta  and  the  energy  given  off  by  the  body  as  heat  and 
muscular  work,  is  the  balance  of  energy,  and,  if  correctly  measured,  should 
equal  the  energy  of  the  body  material  gained  or  lost.  With  such  appara- 
tus it  is  possible  to  learn  what  effect  different  conditions  of  nourishment 
will  have  on  the  human  body.  In  one  experiment,  for  instance,  the  sub- 
ject might  be  kept  quite  at  rest,  and  in  the  next  do  a  certain  amount  of 
muscular  or  mental  work  with  the  same  diet  as  before,  then  by  compar- 
ing the  results  of  the  two,  the  use  which  the  body  makes  of  its  food  under 
the  different  conditions  could  be  determined;  or  the  diet  may  be  slightly 
changed  in  the  one  experiment,  and  the  effect  of  this  on  the  balance  of 
matter  or  energy,  observed.  Such  methods  and  apparatus  are  very  costly 
In  time  and  money,  but  the  results  are  proportionately  more  valuable  than 
those  from  simpler  experiments." 

Fuel  Values  of  Nutrients. —  In  experiments  performed  by  Professor 
Atwater  and  others,  and  in  the  appended  tables,  the  value  of  food  as  a 
source  of  energy  is  stated  in  heat  units  called  calories.  A  calorie  is  the 
amount  of  heat  required  to  raise  the  temperature  of  one  kilogram  of 
water  from  zero  to  one  degree  centigrade.      This  is  about  equivalent  te 


FOODS  321 

raising  one  pound  four  degrees  Fahrenheit.  The  fuel  value  of  different 
foods  may  be  computed  in  a  definite  manner.  This  is  done  by  burning 
a  given  portion  of  a  food  (say  one  pound)  in  the  apparatus  known  as 
the  calorimeter.  By  this  means  may  be  determined  the  number  of  degrees 
the  temperature  of  a  given  amount  of  water  is  raised  during  the  process 
of  burning. 

The  Best  Dietary.  —  Inasmuch  as  all  living  substance  contains 
nitrogen,  it  is  evident  that  proteid  food  must  form  a  part  of  the 
dietary;  but  proteid  alone  is  not  usable.  We  must  take  foods 
that  will  give  us,  as  nearly  as  possible,  the  proportion  of  the 
different  chemical  elements  as  they  are  contained  in  protoplasm. 
We  must  have  a  mixed  diet  which  may  contain  several  different 
food  materials. 

A  growing  person  must  take  in  a  little  more  food  each  day  than 
is  used  up.  In  an  ordinary  day's  work,  a  man  uses  up  about  two 
hundred  and  sixty  grams  of  carbon  and  nineteen  grams  of  nitrogen. 
This  must  be  replaced  in  the  correct  proportion.  More  carbon  or 
more  nitrogen  than  needed,  would  simply  mean  that  some  of  the 
organs  of  the  body  would  have  to  work  overtime  to  rid  the  body 
of  the  unused  material.  It  has  been  found  as  a  result  of  studies  of 
Atwater  and  others,  that  a  man  who  does  muscular  work  requires 
about  one  quarter  of  a  pound  of  proteid,  the  same  amount 
of  fat,  and  about  one  pound  of  carbohydrate  to  provide  for 
the  growth,  waste,  and  repair  of  the  body  and  the  energy 
used  up  in  one  day.  In  addition  to  this,  an  ounce  of  salt  and 
nearly  one  hundred  ounces  of  water  are  used.  The  amount  of 
food  consumed  varies  with  the  age  and  occupation  of  the  individ- 
ual. A  child  of  from  five  to  six  years  needs  only  .5  of  the  food 
required  by  a  man  doing  muscular  work.  A  growing  boy  of  high- 
school  age,  contrary  to  common  belief,  needs  only  between  .7 
and  .8  of  the  food  needed  by  an  active  man.  People  who  lead  a 
sedentary  life  need  much  less  food  than  those  doing  hard  work;  the 
latter,  on  the  other  hand,  need  more  food  than  a  person  who  is  only 
moderately  active.  By  means  of  the  table  on  the  following  page 
(modified  from  Atwater^),  which  shows  the  composition  of  some 
food  materials,  the  nutritive  and  fuel  value  of  the  foods  may  be  seen 

^  W.  O.  Atwater,  Principles  of  Nutrition  and  Nutritive  Value  of  Food.  U.S.  Dept. 
of  Agriculture,  1902. 

hunter's  BIOL.  —  21 


322 


HUMAN   PHYSIOLOGY 


at  a  glance.  The  amount  of  refuse  contained  in  foods  (such  as  the 
bones  of  meat  or  fish,  the  exoskeleton  of  crustaceans  and  mollusks, 
the  woody  coverings  of  plant  cells)  is  also  shown  in  this  table. 


DIGESTIBLE  NOTRIENTS 


INDIGESTIBLE 
NOTRIEKTS 


NON  NUTRIENTS 


PROTEID 


MUSCLE 

MAKING 


FATS  CARBO-      MINERAL 
HYDRATE^  MATTERS 


WATER        REFUSE 


--      FUEL  VALUE 
CALORIES 


FUEL  INGREDIENTS 


NUTRIENTS.  ETC., 
PER  CENT. 


10 

—I — 


20 


30 


40 


50 


60 


70 


80 


90        100 


FUEL  VALUE  OF 
1  LB.  (calories) 


400 


I  '  I  I  I  I  I  I 

800        1,200      2,000     2,200      2,400      2,800     3,200   3,600  4.000 


m 


Milk, 
tinskimmed 

Butter 


White  bread 


Oat  meal 


Com  meal 


Beans 


Table  of  food  values. 


FOODS  323 

A  Mixed  Diet  Best.  —  Knowing  the  proportion  of  the  different 
food  substances  required  by  man,  it  will  be  an  easy  matter  to 
determine  from  this  table  the  best  foods  for  use  in  a  mixed  diet. 
Meats  contain  too  much  nitrogen  in  proportion  to  the  other  sub- 
stances. In  milk,  the  proportion  of  proteids,  carbohydrates,  and 
fat  is  nearly  right  to  make  protoplasm;  a  considerable  amount 
of  mineral  matter  is  also  present.  For  these  reasons,  milk  is 
extensively  used  as  a  food  for  children,  as  it  combines  food 
material  for  the  forming  of  protoplasm  with  mineral  matter  for 
the  building  of  bone.  Some  vegetables  —  for  example,  peas  and 
beans  —  contain  the  nitrogenous  material  needed  for  protoplasm 
formation  in  considerable  proportions,  but  in  a  less  digestible  form 
than  is  found  in  some  other  foods.  Vegetarians  are  correct  in  theory 
when  they  state  that  a  diet  of  vegetables  may  contain  everything 
necessary  to  sustain  life  and  build  tissues.  A  mixed  diet,  however, 
has  been  found  to  be  preferable.  A  purely  vegetable  diet  contains 
much  material,  such  as  the  cellulose  which  forms  the  walls  of  the 
plant  cells,  which  is  indigestible.  Because  of  the  small  amount  of 
proteid  usually  present  in  vegetables,  a  larger  bulk  of  food  material 
is  taken;  thus  the  organs  of  excretion  are  given  increased  work. 
The  Japanese  army  ration  consists  almost  entirely  of  rice.  A  re- 
cent report  by  their  surgeon  general  intimates  that  the  diminutive 
stature  of  the  Japanese  may,  in  some  part  at  least,  be  due  to  this 
diet.  Starch  or  sugar  alone  would  be  an  unwholesome  diet,  because 
of  the  lack  of  nitrogen  and  overabundance  of  carbon. 

Food  Economy.  —  The  American  people  are  far  less  economical  in  their 
purchase  of  food  than  most  other  people.  Nearly  one  half  of  the  total 
income  of  the  average  working  man  is  spent  on  food.  Not  only  does  he 
spend  a  large  amount  on  food  but  he  wastes  money  in  purchasing  the 
wrong  kinds  of  food.  The  table  on  the  following  page  (modified  from 
Atwater),^  shows  how  economy  may  be  exercised  in  the  purchase  of  foods. 

Adulterations  in  Foods.  —  Many  foods  which  are  artificially  manufac- 
tured have  been  adulterated  to  such  an  extent  as  to  be  almost  unfit  food 
or  even  harmful.  One  of  the  commonest  adulterations  is  the  substitution 
of  grape  sugar  (glucose)  for  cane  sugar.  Most  cheap  candy  is  so  made. 
Flour  and  other  cereal  foods  are  frequently  adulterated  with  some  cheap 

1  W.  O,  Atwater,  Principles  of  Nutrition  and  Nutritive  Value  of  Food.  U.S. 
Dept.  of  Agriculture,  1902. 


324 


HUMAN  PHYSIOLOGY 


PROTEID 


PATS 


CARBOHYDRATES 


FUEL  VALUE 


FOOD 
MATERIALS 


K 


POUNDS 


POUNDS  OF  NUTRIENTS  AND  CALORIES  OF  FUEL  VALUE 
IN  10  CENTS  WORTH 


1  LB. 


2  LBS. 


3  LBS. 


2,000  GAL. 


4.000  CAL. 


6. 000  GAL. 


Eeef,  round 


14 


.71 


Si 


Beef,  sirloin 


20 


.50 


S 


Beef,  shoulder 


12 


.83 


Mutton,  leg 


16 


.63 


Pork,  loin 


12 


.83 


Pork,  salt,  fat 


12 


.83 


Ham,  smoked 


18 


.56 


Codfish,  fresh, 
dressed 


10 


1.00 


Oysters  35  cents 
per  quart 


18 


.56 


Milk,  6  cents 
per  quart 


3.33 


Butter 


25 


.40 


Cheese 


16 


.63 


Eggs,  24  cents 
per  dozen 


16 


.63 


i 


Wheat  bread 


2.00 


Corn  meal 


2K 


4.00 


Oat  meal 


2.50 


Beans,  white,  dried 


2.00 


Rice 


1.25 


.M. 


Potatoes,  60  cents 
per  bushel 


10.00 


Sugar 


1.67 


y/////y,y. 


Table  showing  the  cost  of  nutrients. 

substitute;  the  list  of  adulterated  articles  is  almost  inexhaustible, 
food  laws  have  been  passed  by  Congress,  which  strike  at  this  evil. 


Pure- 


FOODS  325 

Impure  Water.  —  One  danger  far  greater  than  the  abova-mentioned 
comes  from  drinking  impure  water.  This  subject  has  already  been  dis- 
cussed under  Bacteria,  where  it  was  seen  that  the  spread  of  typhoid  fever 
in  particular  is  due  to  a  contaminated  water  supply.  As  citizens  we 
must  aid  all  legislation  that  will  safeguard  the  water  used  by  our  towns 
and  cities.  Boiling  water  for  ten  minutes  or  longer  will  render  it  safe 
from  all  organic  impurities. 

Food  Waste  in  the  Kitchen.  —  Much  loss  occurs  in  the  improper  cook- 
ing of  foods.  Meats  especially,  when  overdone,  lose  much  of  their  flavor 
and  are  far  less  easily  digested  than  when  they  are  cooked  rare.  The 
chief  reasons  for  cooking  meats  are  that  the  muscle  fibers  may  be  loosened 
and  softened,  and  that  the  bacteria  or  other  parasites  in  the  meat  may 
be  killed  by  the  heat.  The  common  method  of  frying  makes  foods  less 
digestible.  Stewing  is  an  economical  as  well  as  healthful  method,  A  good 
way  to  prepare  meat,  either  for  stew  or  soup,  is  to  place  the  meat,  in  small 
pieces,  in  cold  water,  and  allow  it  to  simmer  for  several  hours.  Rapid  boil- 
ing toughens  the  muscle  fibers  by  the  too  rapid  coagulation  of  the  albumin- 
ous matter  in  them,  just  as  the  white  of  egg  becomes  solid  when  heated^ 
Broiling  and  roasting  are  excellent  methods  of  cooking  meat.  In  order  to 
prevent  the  loss  of  the  nutrients  in  roasting,  it  is  well  to  baste  the  meat  fre- 
quently; thus  a  crust  is  formed  on  the  outer  surface  of  the  meat,  which 
prevents  the  escape  of  the  juices  from  the  inside. 

Vegetables  are  cooked  in  order  that  the  cells  containing  starch  grains 
may  be  burst  open,  thus  allowing  the  starch  to  be  more  easily  attacked 
by  the  digestive  fluids.  Inasmuch  as  water  may  dissolve  out  nutrients 
from  vegetable  tissues,  it  is  best  to  boil  them  rapidly  in  a  small  amount 
of  water.  This  gives  less  time  for  the  solvent  action  to  take  place.  Veg- 
etables should  be   cooked  with  the  outer  skin  left  on  when  it  is  possible. 

Stimulants.  —  V^e  have  learned  that  food  is  anything  that  sup- 
plies building  material  or  releases  energy  in  the  body;  but  some 
materials  used  by  man,  presumably  as  food,  do  not  come  under 
this  head.  Such  are  tea  and  coffee.  When  taken  in  moderate 
quantities,  they  produce  a  temporary  increase  in  the  vital 
activity  of  the  person  taking  them.  This  is  said  to  be  a  stimula- 
tion; and  material  taken  into  the  digestive  tract,  producing  this, 
is  called  a  stimulant.  In  moderation,  tea  and  coffee  appear  to  be 
harmless.  Some  people,  however,  cannot  use  either  without  ill 
effects.  It  is  the  habit  formed  of  relying  upon  the  stimulus  given 
by  tea  or  coffee,  that  makes  them  a  danger  to  man.  In  large 
amounts,  they  are  undoubtedly  injurious  because  of  a  substance, 
called  caffeine,  contained  in  them. 


326  HUMAN   PHYSIOLOGY 

Alcohol.  —  The  question  of  the  use  of  alcohol  has  been  of 
late  years  a  matter  of  absorbing  interest  and  importance  among 
physiologists.  Dr.  Atwater  performed  a  series  of  very^  careful 
experiments  by  means  of  the  respiration  calorimeter,  to  ascertain 
if  alcohol  is  of  use  to  the  body  as  food.^  In  these  experiments, 
the  subjects  were  given,  instead  of  their  daily  allotment  of  carbo- 
hydrates and  fats,  enough  alcohol  to  supply  the  same  amount  of 
energy  that  these  foods  would  have  given.  The  amount  was  calcu- 
lated to  be  about  two  and  one  half  ounces  per  day,  about  as  much 
as  would  be  contained  in  a  bottle  of  light  wine.^  This  alcohol  was 
administered  in  small  doses  six  times  during  the  day.  Professor 
Atwater's  results  may  be  summed  up  briefly  as  follows:  — 

1.  The  alcohol  administered  was  almost  all  oxidized  in  the 
body. 

2.  The  potential  energy  in  the  alcohol  was  transformed  into  heat 
or  muscular  work. 

3.  The  body  did  about  as  well  with  the  rations  including  alcohol 
as  it  did  without  it. 

The  committee  of  fifty  eminent  men  appointed  to  report  on  the 
physiological  aspects  of  the  drink  problem,  reported  that  a  large 
number  of  scientific  men  state  that  they  are  in  the  habit  of  taking 
alcoholic  liquor  in  small  quantities,  and  many  report  that  they  do 
not  feel  harm  thereby.  A  number  of  scientists  seem  to  agree  that, 
within  limits,  alcohol  may  be  a  kind  of  food,  although  a  very  poor 
food.     The  following  statements  support  this  view:  — 

"The  conclusion  to  which  all  the  evidence  points  is  that  alcohol  is  a  food, 
and  in  certain  circumstances,  such  as  febrile  conditions,  it  may  be  a  very- 
useful  food;  but  in  health,  when  other  kinds  of  food  are  abundant,  it  is 
unnecessary,  and  as  it  interferes  with  oxidation,  it  is  an  inconvenient  kind 
of  food."  —  T.  Lauder-Brunton,  A  Text-book  of  Pharmacology,  Thera- 
peutics and  Materia  Medica  (London,  1887),  page  768. 

"If  oxidized  even  to  a  small  extent,  and  the  evidence,  as  indicated, 
points  to  the  oxidation  of  by  far  the  larger  proportion  of  it,  ninety  five 
per  cent  alcohol  must  be  regarded  in  the  scientific  sense  as  a  food.  .  .  . 

*  Alcohol  is  made  up  of  carbon,  oxygen,  and  hydrogen.  It  is  very  easily  oxidized, 
but  it  cannot,  as  is  shown  by  the  chemical  formula,  be  of  use  to  the  body  in  tissue 
building  because  of  its  lack  of  nitrogen. 

^  Alcoholic  beverages  contain  the  following  proportions  of  alcohol :  beer,  from 
2  to  5  per  cent;  wine,  from  10  to  20  per  cent;  liquors,  from  30  to  70  per  cent. 
Patent  medicines  frequently  contain  as  high  as  60  per  cent  alcohol. 


FOODS  327 

While,  therefore,  it  must  be  classed  technically  as  a  food,  it  is  in  many 
respects  an  unsuitable  food,  and  its  place  can  be  taken  with  great  advan- 
tage by  other  substances."  —  Kendrick,  Physiology  (Glasgow,  1889), 
Vol.  II,  page  19. 

"Alcohol  is  thus,  within  narrow  limits,  a  food.  ...  It  is,  moreover,  a 
very  uneconomical  food.  Much  more  nutriment  would  have  been  obtained 
from  the  barley  or  curds  from  which  it  was  made.  The  value  of  alcohol 
within  narrow  limits  is  not  as  a  food,  but  as  a  stimulant,  not  only  to  diges- 
tion, but  to  the  heart  and  brain." — Halliburton,  Text-hook  of  Chemical 
and  Pathological  Physiology,  1891,  page  600. 

"  According  to  Dupre,  one  grain  of  alcohol  oxidized  in  the  body  evolves 
7134  units  of  heat,  while  the  same  amount  of  lean  beef  gives  off  only  1482 
units  of  heat.  It  has  been  estimated  that  9.5  ounces  of  lean  beef  (equal 
to  about  2  ounces  of  alcohol)  will  supply  the  force  necessary  to  maintain 
the  circulation  and  respiration  for  one  day.  That  is,  four  ounces  of  strong 
spirit  will  suffice  for  this  purpose.  These  considerations  warrant  the 
statement  that,  in  a  certain  sense,  alcohol  is  a  food,  i.e.  that  it  is  capable 
of  being  used  for  the  purpose  of  the  organism."  —  H.  C.  Wood,  Therapeu- 
tics. 

''Alcohol  in  small  doses  is  of  great  use  in  conditions  of  temporary  want  or 
where  food  is  taken  in  insufficient  quantity.  When  alcohol  is  taken  regu- 
larly, more  especially  in  large  doses,  it  affects  the  nervous  system  and 
undermines  the  physical  and  corporal  faculties,  partly  by  the  action  of 
the  impurities  which  it  may  contain,  such  as  fusel  oil,  which  has  a  poisonous 
effect  on  the  nervous  system;  partly  by  its  direct  effects,  such  as  catarrh 
and  inflammation  of  the  digestive  organs,  which  it  produces;  and  lastly 
by  its  effects  on  the  normal  metabolism."  —  Landois  &  Sterling,  Text- 
hook  on  Human  Physiology  (London,  1891),  page  437. 

On  the  other  hand,  we  know  that  although  alcohol  may  techni- 
cally be  considered  as  a  food,  it  is  a  very  unsatisfactory  food.  In 
large  doses,  it  is,  undoubtedly,  poisonous.  A  commonly  accepted 
definition  of  a  poison  is  that  it  is  any  substance  which,  when  taken 
into  the  body,  tends  to  cause  serious  detriment  to  health  or  the  death 
of  the  organism. 

That  alcohol  may  do  this  is  well  known  by  scientists.  The 
following  quotations  show  that  a  large  number  of  very  eminent 
professors  and  physicians  have  this  belief. 

"  From  an  exhaustive  definition  we  shall  have  to  class  every  substance  as 
a  poison  which,  on  becoming  mixed  with  the  blood,  causes  a  disturbance 
in  the  function  of  any  organ.  That  alcohol  is  such  a  poison  cannot  be 
doubted.  .   .  .     Very  appropriately  has  the  English  language   named  the 


328  HUMAN   PHYSIOLOGY 

disturbance  caused  by  alcoholic  beverages  intoxication,  which,  by  deriva- 
tion, means  poisoning."  —  Dr.  Adolph  Fick,  Professor  of  Physiology,  Wiirz- 
burg,  Germany. 

"Ethyl  alcohol,  even  when  diluted  as  in  wine,  beer,  and  cider,  is  a  poison 
which  changes  pathologically  the  tissues  of  the  body  and  leads  to  fatty 
degeneration.  Of  course  I  am  not  speaking  here  of  the  smallest  doses. 
However,  the  latter  (for  example,  half  a  liter  of  beer  or  a  glass  of  wine) 
are  also  poisonous,  because  they  injure  the  brain  by  producing  paralysis 
and  derangement  of  function;  that  is  clearly  demonstrated  by  the  experi- 
ments of  Kraepelin,  Smith,  Fiirer,  Aschaffenburg,  etc.  The  same  have 
never  been  controverted.  The  most  moderate  drinking  of  alcohol  is  quite 
useless  for  the  individual,  but  by  means  of  example  and  fashion  produces 
an  incalculable  social  injury  and  misery  to  the  masses,  since  all  cannot 
remain  moderate,  and  the  entirely  moderate  remains  at  last  the  exception.'' 
—  Dr.  August  Forel,  Professor  of  Psychiatry  in  the  University  of  Zurich. 

"All  the  alcohols  are  poisons."  —  Dujardin-Beaumetz  and  Audtge. 

"Is  alcohol  a  poison?  I  reply.  Yes.  It  answers  to  the  description  of  a 
poison.  It  possesses  an  inherent  deleterious  property  which,  when  intro- 
duced into  the  system,  is  capable  of  destroying  life,  and  it  has  its  place  with 
arsenic,  belladonna,  prussic  acid,  opium,  etc." — Dr.  Willard  Parker,  late 
Professor  of  Surgery  in  the  College  of  Physicians  and  Surgeons,  New  York; 
Consulting  Physician  to  Bellevue,  Mount  Sinai,  Roosevelt,  and  the  New 
York  hospitals. 

"  It  [alcohol]  leads  to  degeneration  of  the  tissues;  it  damages  the  health; 
it  injures  the  intellect.  Short  of  drunkenness,  that  is,  in  those  effects  of 
it  which  stop  short  of  drunkenness,  I  should  say  from  my  experience  that 
alcohol  is  the  most  destructive  agent  we  are  aware  of  in  this  country." — • 
Sir  William  Gull,  M.D.,  F.R.S.,  Consulting  Physician  to  Guy's  Hospital, 
London. 

"  We  know  that  alcohol  is  mostly  oxidized  in  our  body.  .  .  .  Alcohol  is, 
therefore,  without  doubt,  a  source  of  living  energy  in'  our  body,  but  it 
does  not  follow  from  this  that  it  is  also  a  nutriment.  To  justify  this  assump- 
tion, proof  must  be  furnished  that  the  living  energy  set  free  by  its  oxida- 
tion is  utilized  for  the  purpose  of  a  normal  function.  It  is  not  enough 
that  potential  energy  is  transformed  into  living  energy;  the  transformation 
must  take  place  at  the  right  time  and  place,  and  at  definite  points  in  definite 
elements  of  the  tissues.  These  elements  are  not  adapted  to  be  fed  with 
every  sort  of  oxidizable  material.  We  do  not  know  whether  alcohol  can 
furnish  to  the  muscles  and  nerves  a  source  of  energy  for  the  performance 
of  their  functions.  ...  In  general,  alcohol  has  only  paralyzing  proper- 
ties, etc."  —  G.  Bunge,  Lehrbuch  der  Physiologischen  und  Pathologischen 
Chemie  (Leipsic,  1894),  page  124. 

"Alcohol,  also,  when  not  taken  in  too  large  quantities,  maybe  oxidized 
in  the  body,  and  furnish  a  not  inconsiderable  amount  of  energy.     It  i^ 


FOODS  329 

however,  a  matter  of  controversy  at  present,  whether  alcohol  in  small 
doses  can  be  considered  a  true  foodstuff  capable  of  serving  as  a  direct 
source  of  energy,  and  of  replacing  a  corresponding  amount  of  fats  and 
carbohydrates  in  the  daily  diet."  —  William  H.  Howell,  American  Text- 
book of  Physiology  (Philadelphia,  1896),  page  297. 

"The  nutritive  value  of  alcohol  has  been  the  subject  of  considerable  dis- 
cussion and  not  a  few  experiments.  Some  of  these  tend  to  show  that  in 
moderate  non-poisonous  doses  it  acts  as  a  non-proteid  food  in  diminishing 
the  oxidation  of  proteid,  doubtless  by  becoming  itself  oxidized.  Its  aci-ion, 
however,  in  this  respect,  is  relatively  small,  and,  indeed,  a  certain  propor- 
tion of  the  alcohol  ingested  is  exhaled  with  the  air  of  respiration. 

"Moreover,  in  large  doses  it  [alcohol]  may  act  in  a  contrary  manner, 
increasing  the  waste  of  tissue  proteid.  It  cannot,  in  fact,  be  doubted  that 
any  small  production  of  energy  resulting  from  its  oxidation  is  more  than 
counterbalanced  by  its  deleterious  influence  as  a  drug  upon  the  tissue  ele- 
ments, and  especially  upon  those  of  the  nervous  system."  —  E.  A.. 
ScHAEFER,  A  Text-book  of  Physiology  (1898),  page  882. 

The  Use  of  Tobacco.  —  A  well-known  authority  defines  a  nar- 
cotic as  a  substance  ''  which  directly  induces  sleep,  blunts  the 
senses,  and,  in  large  amounts,  produces  complete  insensibility  " 
Tobacco,  opium,  chloral,  and  cocaine  are  examples  of  nar- 
cotics. Tobacco  owes  its  narcotic  influence  to  a  strong  poison 
known  as  nicotine.  In  experiments  with  jellyfish  and  other 
lowly  organized  animals,  the  author  has  found  as  small  a  per 
cent  as  one  part  of  nicotine  to  one  hundred  thousand  parts 
of  sea  water  to  be  sufficient  to  profoundly  a^ffect  an  animal 
placed  within  it.  Nicotine  in  a  pure  form  is  so  powerful  a  poison 
that  two  or  three  drops  would  be  sufficient  to  cause  the  death  of  a 
man  by  its  action  upon  the  nervous  system,  especially  the  nerves 
controlling  the  beating  of  the  heart.  This  action  is  well  known 
among  boys  training  for  athletic  contest.  The  heart  is  affected, 
boys  become  ^' short  winded''  as  a  result  of  the  action  on  the 
heart.  It  has  been  demonstrated  that  tobacco  has,  too,  an 
important  effect  on  muscular  development.  The  stunted  appear- 
ance of  the  young  smoker  is  well  known. 


XXVIII.     DIGESTION  AND   ABSORPTION 


Purpose  of  Digestion.  —  We  have  learned  that  starch  and  proteid 
food  of  plants  are  formed  in  the  leaves.  A  plant,  however,  is 
unable  to  make  use  of  the  food  in  this  condition.     Before  it  can 

be  used  it  is  changed  into  a 
soluble  form,  such  as  grape 
sugar.  In  this  state  it  can 
be  passed  from  cell  to  cell 
by  the  process  of  osmosis, 
and  can  be  used  to  build 
new  cells  or  to  release  energy. 
The  same  condition  exists  in 
animals.  In  order  that  food 
may  be  of  use  to  man,  it 
must  be  changed  into  a  state 
that  will  allow  of  its  passage 
in  a  soluble  form  through 
the  walls  of  the  alimentary 
canal  or  food  tube.  Diges- 
tion consists  in  the  changing 
of  foods  from  an  insoluble  to 
a  soluble  form,  so  that  they  may 
pass  through  the  walls  of  the 
alimentary  canal  and  become 
part  of  the  blood. 

Alimentary  Canal.  —  In  all 
vertebrate  animals,  including 
man,  food  is  normally  taken 
in  the  mouth  and  passed  through  a  food  tube  during  the  process 
of  digestion.  This  tube  is  composed  of  different  portions,  named, 
respectively,  as  we  pass  from  the  mouth,  posteriorly,  the  gullet, 
stomach,  small  and  large  intestine,  and  rectum. 

330 


m- 


Picture  of  the  organs  of  digestion;  a,  intestine, 
leading  out  of  the  pylorus;  6,  liver;  c,  esoph- 
agus; d,  pancreas;  e,  stomach;  /,  spleen; 
g,  i,  j,  k,  m,  n,  parts  of  large  intestine; 
h,  I,  small  intestine.  From  Johonnot  and 
Bouton. 


DIGESTION    AND   ABSORPTION 


33i 


Glands.  —  In  addition  to  the  alimentary  canal  proper,  we  find  a 
number  of  digestive  glands,  varying  in  size  and  position,  connected 
with  the  canal.  A  gland  is  a  collection  of  cells  which  takes  up 
materials  from  the  blood  and  pours  out  the  secretion  as  a  fluid; 
such  cells,  together  with  the  blood  vessels  and  nerves  passing  to 
them,  are  held  in  place  by  a  web  of  connective  tissue. 

It  is  the  substances  formed  by  these  glands  that  cause  the  di- 
gestion of  food.  The  substances  secreted  by  the  cells  of  the  glands 
and  poured  out  into  the  food  tube  act  upon  insoluble  foods  so  as 
to  change  them  to  a  soluble  form. 

Structure.  —  The  entire  inner  surface  of  the  food  tube  is  covered  with  a 
soft  lining  of  mucous  membrane.  This  is  always  moist  because  certain  cells, 
called  mucous  cells,  empty  out  their  con- 
tents into  the  food  tube,  thus  lubricating 
its  inner  surface.  When  a  large  number 
of  cells  which  have  the  power  to  secrete 
or  form  fluids  are  collected  together, 
the  surface  of  the  food  tube  may  be- 
come indented;  the  little  depression 
thus  formed  is  a  simple  gland.  If  such 
a  tube  is  greatly  branched,  with  one 
common  duct  or  tube  connecting  it 
with  the  inside  surface  of  the  food  tube, 
it  is  then  called  a  compound  gland.  If 
we  think  of  a  very  sour  pickle  or  a  de- 
licious bit  of  candy,  our  mouth  waters. 
This  is  caused  by  the  action  of  certain 
nerves  upon  some  of  the  gland  cells  in 
the  mouth  (salivaric  glands) ;  this  re- 
sults in  the  setting  free  of  a  fluid  we 
call  saliva.  In  case  of  stage  fright,  the 
secretion  of  saliva  is  prevented  by  the  action  of  the  nervous  system,  and 
fche  mouth  becomes  dry. 

Comparison  of  the  Alimentary  Canal  of  a  Frog  with  that  op 
Man.^ — (Material  —  frogs  preserved  in  alcohol  or  four  per  cent  formol.) 
Notice  the  shape  and  size  of  the  mouth  when  closed  and  when  opened. 
Look  for  teeth.  Feel  with  your  finger  the  upper  and  lower  jaws  in  the 
roof  Oi"  the  mouth.  The  prominent  teeth  on  the  roof  of  the  mouth  are 
known  as  the  vomerine  teeth.  Notice  the  mucous  membrane  lining  in 
the  interior  of  the  mouth.  With  a  pencil  or  tweezers,  find  the  baglike 
openmg  of  the  gullet  through  which  food  passes  to  the  stomach.     Do  not 


Structure  of  glands;  1,  simple  pit,  sur- 
rounded by  capillaries;  2,  flask- 
shaped  gland,  with  short  duct ;  3,  4, 
more  complex  glands,  with  longer 
ducts. 


'  For  more  detailed  work,  see  Hunter  and  Valentine,  Manual,  pp.  174-177. 


332 


HUMAN   PHYSIOLOGY 


confuse  this  with  the  much  smaller  glottis,  a  longitudinal  slit  opening  into 
the  windpipe.  Other  paired  openings  are  found  in  the  mouth,  those  lead- 
ing to  the  anterior  nares  or  external  nostril  openings  and  those  leading  to 
the  ear,  the  Eustachian  tubes.  Make  a  drawing  of  the  open  mouth  of  a  frog, 
showing  these  points. 

Buccal  Cavity  in  Man.  —  In  man,  the  mouth,  or  buccal  cavity,  is 
lined  with  mucous  membrane.  Mucous  membrane,  because  it  is 
thinner  than  the  skin,  allows  the  blood  to  show  through,  thus 
giving  the  characteristic  red  color  of  the  lips  and  inner  mouth. 
The  roof  of  the  mouth  is  formed  by  a  plate  of  bone  called  the  hard 
palate.  This  separates  the  nose  cavity  from  that  of  the  mouth 
proper.  Behind  the  hard  palate  the  cavities  are  separated  by  the 
soft  palate.  The  part  of  the  mouth  cavity  back  of  the  soft  palate 
is  called  the  pharynx.  From  the  pharynx  lead  off  the  gullet  and 
'Windpipe,  the  latter  placed  ventral  to  the  former.  The  lower  part 
of  the  buccal  cavity  is  almost  filled  by  a  muscular  tongue.  Ex- 
amination of  its  surface  with  a  looking  glass  shows  it  to  be  almost 
covered  in  places  by  tiny  projections  called  papillce.  These  papil- 
lae contain  organs  known  as  taste  hicds,  the  sensory  endings  of 
which  determine  the  taste  of  substances.  The  tongue  is  also 
used  in  moving  food  about  in  the  mouth,  in  starting  it  on  its  way 

to  the  gullet,  while  it  plays 
an  important  part,  as  we 
know,  in  speaking. 

The  Teeth.  —  Plainly  the 
teeth  of  a  frog  are  not  used 
for  cutting  or  grinding  up 
food;  they  point  inward, 
a  significant  fact  which 
shows  them  to  be  used  for 
holding.  The  teeth  of  man 
are  divided,  according  to 
their  functions,  into  four 
groups.  In  the  center  of 
both  the  upper  and  lower  jaw  in  front  are  found  eight  teeth  with 
chisel-like  edges;  these  are  the  incisors,  or  cutting  teeth.  Next 
is  found  a  single  tooth  on  each  side  (four  in  all) ;  these  have  rather 
sharp  points;  they  are  the  canines;  look  for  them  in  a  cat  or  dog. 


Teeth;  a,  incisors;  6,  canine;  c,  premolars; 
d,  molars. 


DIGESTION   AND   ABSORPTION 


333 


Then  come  two  teeth  on  each  side,  called  premolars.  Lastly,  the 
flat-topped  molars,  or  grinding  teeth.  Food  is  caught  between  ir- 
regular projections  on  the  surface  of  the  molars  and  crushed  to  a 
pulpy  mass. 

Laboratory  Exercise.  —  Procure  from  the  dentist  examples  of  each  kind  of 
teeth.     Identify  and  draw  in  your  notebook  one  of  each  of  the  four  classes. 

Dental  Formula  of  Man.  —  It  is  possible,  as  we  have  seen,  to  classify 
mammals  partially  on  the  basis  of  the  kind  and  number  of  teeth  they 
possess.  The  number  of  these  teeth  may  be  graphically  shown  by  means 
of  what  is  called  a  dental  formula.  In  a  dental  formula,  the  teeth  of  the 
upper  jaw  (the  right  and  left  sides  separately)  form  the  numerator  of  the 
fraction;  those  of  the  lower  jaw  form  the  denominator.  This  dental 
formula  of  man  is  graphically  shown  as  follows :  — 


incisors 


2  +  2  . 
2  +  2  ' 

premolars  =  — ^^  : 
^  2  +  2  ' 


camnes  = 


molars  = 


1  +  1  . 
1  +  1' 
3+3  . 
3  +  3  ' 


total,  32. 


Man  differs  from  other  vertebrate  animals  in  that  when  young  the  child 
has  a  set  of  teeth  which  later  fall  out  and  are  replaced  by  the  thirty-two 
teeth  known  as  the  permanent  set. 

The  first  set,  known  as  the  milk  teeth,  consists  of  twenty  teeth  arranged 
as  follows :  — 


mcisors 


2+2  .  1+1  1  2+2 

=  :        canines  =  :        molars  =  — ' —  ; 

2  +  2  1  +  1  2  +  2 


total,  20. 


The  permanent  teeth  appear  to  push  out  the  milk  teeth ;  this  is  indeed 
the  case,  as  the  beginnings  of  the  permanent  teeth  are  found  very  early  in 
life  under  the  milk  teeth.  The  so-called  wisdom  teeth  (four  molars)  do 
not  appear  until  the  eighteenth  to  the  twenty-first  year  of  life. 

Internal  Structure  of  a  Tooth.  —  If  a  tooth  is  cut 
lengthwise,  it  is  found  to  be  hollow;  this  cavity,  called 
the  pulp  cavity,  corresponds  to  the  cavity  containing 
marrow  in  bones.  In  life  it  contains  living  material  — 
the  blood  vessels,  nerves,  and  cells  which  build  up  the 
bony  part  of  the  tooth.  The  bulk  of  the  hard  part  of 
the  tooth  consists  of  a  limy  material  called  dentine.  Out- 
side of  this  is  a  very  hard  substance  called  enamel;  this 
substance,  the  hardest  in  all  the  body,  is  thickest  on  the 
exposed  surface  or  crown  of  the  tooth.  What  is  the  use 
of  this  hard  layer?  Why  is  it  so  placed?  Each  tooth 
is  held  in  its  place  in  the  jawbone  by  a  thin  layer  of 
bony  substance  called  cement. 


Section  of  a  tooth; 
a,  enamel;  b, 
dentine;  c.  pulp 
cavity  contain- 
ing blood  ves- 
sels and  nerves; 
d,  cement. 


334  HUMAN   PHYSIOLOGY 

Salivary  Glands.  —  Besides  the  cells  in  the  mouth  which  secrete 
mucus,  other  collections  of  gland  cells  form  a  substance  called 
saliva.  There  are  three  pairs  of  the  salivary  glands.  They  are 
named  according  to  their  position,  the  parotid  (under  the  ear),  the 
submaxillary  (under  the  jawbone),  and  the  sublingual  (under  the 
tongue) . 

Home  Exercise.  —  Chew  paraffin  or  India  rubber  and  collect  saliva  in 
a  test  tube.  Answer  the  following  questions.  What  is  its  color?  Does 
any  sediment  appear  after  standing  ?  Test  with  htmus  paper  for  its  chemical 
reaction.  Partly  fill  three  test  tubes,  one  with  water,  one  with  saliva,  one 
with  saliva  plus  weak  acetic  acid.  Place  in  each  a  small  piece  of  cracker. 
Leave  the  three  overnight  in  a  warm  place  (about  98°  Fahrenheit).  Next 
morning  test  the  contents  of  the  tubes  for  starch  and  for  grape  sugar. 
In  which  tube  has  some  starch  been  changed  to  grape  sugar?  Chew  a 
piece  of  cracker  slowly.  Notice  any  change  in  taste  of  cracker.  How  do 
you  account  for  this  ? 

Digestion  of  Starch.  —  The  digestion  of  starch  to  grape  sugar 
is  caused  by  the  presence  in  the  saliva  of  an  enzyme,  or  digestive 
ferment.  You  will  remember  that  starch  in  the  growing  corn 
grain  was  changed  to  grape  sugar  by  an  enzyme,  called  diastase. 
Here  the  same  action  is  caused  by  an  enzyme  called  vtyalin. 
This  ferment,  as  we  see,  acts  only  in  an  alkaline  medium  at  about 
the  temperature  of  the  body. 

Openings  from  Buccal  Cavity.  —  The  mouth  cavity  of  man,  as  that  of 
a  frog,  has  four  paired  openings  leading  from  it,  —  two  into  the  nostril  (the 
'posterior  nares),  and  two  to  the  ear  (the  Eustachian  tubes,  named  after  their 
discoverer,  an  Italian  doctor).  Three  single  openings  also  exist, — one  to 
the  outside   (the  mouth),  another  to  the  lungs,  and  a  third,  the  gullet. 

In  man,  the  windpipe  is  easily  felt.  It  is  a  cartilaginous  tube,  the  upper 
part  forming  the  voice  box,  or  larynx  (Adam's  apple);  directly  dorsal  to 
this  is  the  gullet.  Food,  in  order  to  reach  the  gullet  from  the  mouth  cavity, 
must  pass  over  the  glottis,  the  opening  into  the  trachea.  In  the  frog,  the 
glottis  is  normally  a  closed  slit.  In  man,  it  is  proportionately  much  wider. 
When  food  is  in  the  course  of  being  swallowed,  the  upper  part  of  the  larynx, 
called  the  epiglottis,  forms  a  trap  door  over  the  opening.  When  the  epi- 
glottis is  not  closed,  and  food  "goes  down  the  wrong  way,"  we  choke 
and  the  food  is  expelled  by  coughing. 

The  Gullet,- or  Esophagus.  —  In  man  this  part  of  the  food  tube  is  much 
longer  proportionately  than  in  the  frog.  Like  the  rest  of  the  food  tube 
it  is  lined  by  soft  and  moist  mucous  membrane.  The  wall  is  made  up  of 
two  sets  of  muscles,  —  the  inside  ones  running  around  the  tube;  the  outer 
band  of  muscle  taking  a  longitudinal  course.     After  food  leaves  the  mouth 


DIGESTION   AND   ABSORPTION 


335 


cavity,  it  gets  beyond  our  direct  control ;  the  muscles  of  the  gullet,  stimu- 
lated to  activity  by  the  presence  of  food  in  the  tube,  push  the  food  down 
to  the  stomach  by  a  series  of  contractions. 


Opening  of 
Eustachian  tube  — 


Soft  palate 


Hard  palate 


Pharynx  — 


Tongue 


Vertical  section  of  the  head  and  neck. 

Demonstration. — Cut  away  the  throat  muscles  of  a  frog  so  as  to  expose 
the  windpipe,  or  trachea;  under  this  is  a  soft  tube  much  wider  in  extent, 
the  gullet. 

Stomach  of  Frog.  —  Make  a  median  cut  through  the  muscles  on  the  ven- 
tral side  of  the  abdomen  of  a  frog;  then  make  incisions  at  right  angles  to 
this,  just  below  the  fore  legs  and  immediately  in  front  of  the  hind  legs. 
Fold  back  the  outer  skin  and  the  muscles  and  pin  them  into  place  at  the  dor- 
sal side  of  the  body.  Notice  the  thin  glistening  membrane  lining  the  cavity 
inside  the  body.  This  is  called  the  peritoneum.  The  peritoneum  forms  a 
fold  on  the  dorsal  side  of  the  body  cavity  (called  the  mesentery),  and  in 
this  incloses  all  the  organs  of  digestion,  etc.,  so  that  they  hang  from  the 
dorsal  side  when  the  animal  is  in  natural  position.  The  peritoneum  and 
mesentery  are  present  in  man. 

The  stomach  may  easily  be  found  after  lifting  up  the  dark  red,  three- 
lobed  liver.  Note  the  position  and  size  of  the  stomach.  This  will  vary 
considerably  according  to  the  amount  of  food  inside. 

Stomach  of  Man.  —  In  man,  the  stomach  has,  in  general,  the 
same  position  as  in  the  frog.  This  difference,  however,  exists: 
The  gullet  passes  directly  through  a  muscular  partition,  the  dia- 
phragm, which  is  lacking  in  the  frog.     The  diaphragm  separates 


336 


HUMAN   PHYSIOLOGY 


Inside  of  the  stomach  and  intestine,  show- 
ing the  folds  of  the  mucous  membrane. 


the  heart  and  lungs  from  the 
other  organs  of  the  body  cavity. 
The  stomach  is  a  pear-shaped 
organ  capable  of  holding  about 
three  pints.  The  end  opposite  to 
the  gullet,  which  empties  into 
the  small  intestine,  is  provided 
with  a  valve  called  the  pylorus. 

Demonstration  —  Open  the  stom- 
ach of  the  frog;  remove  its  contents 
by  carefully  washing.  The  stomach 
wall  is  seen  to  be  thrown  into  folds 
internally. 


Gastric  Glands.  —  Between  these  folds,  in  the  stomach  of  man 
as  well  as  in  the  frog,  are  located  a  number  of  tiny  pits.  These 
form  the  mouths  of  the  gastric  glands,  which  pour  into  the  stomach 
a  secretion  known  as  the  gastric  juice.  The 
gastric  glands  are  little  tubes,  the  lining  of  which 
secretes  the  fluid.  This  fluid  is  largely  water. 
It  is  slightly  acid  in  its  chemical  reaction.  (It 
contains  about  .2  per  cent  free  hydrochloric  acid.) 
It  also  contains  a  very  important  enzyme  called 
pepsin,  and  another  less  important  one  called 
rennin. 


The  action  of  gastric  juice  upon  proteids  may  be  de- 
termined by  the  following  experiment.  Number  five 
test  tubes,  1  to  5  inclusive. 

In  No.  1  place  minced  white  of  egg  +  water. 

In  No.  2  place  minced  white  of  egg  +  .2  per  cent 
hydrochloric  acid. 

In  No.  3  place  minced  white  of  egg  +  .2  per  cent 
hydrochloric  acid  and  pepsin. 

Treat  No.  4  and  No.  5  as  No.  3. 

Place  Nos.  1,2,  and  3  in  a  water  bath  (or  in  a  pail  of 
water  over  a  radiator  or  register)  where  the  tempera- 
ture will  stand  at  about  982°  Fahrenheit  for  several 
hours. 

Place  No.  4  in  the  ice  box  or  surround  with  ice  for 
three  hours.  Place  No.  5  in  boiling  water  for  half  an 
hour,  then  place  with  Nos.  1,  2,  and  3. 

Note  all  changes  that  have  taken  place  in  the  differ- 
ent tubes. 


A  peptic  gland,  from 
the  stomach,  very 
much  magnified. 
A,  central  or  chief 
cells,  which  make 
pepsin;  B,  border 
cells,  which  make 
acid.  From  Mil- 
ler's Histology. 


DIGESTION   AND   ABSORPTION  337 

Test  the  contents  of  the  different  tubes  for  peptone  with  the  biuret  test. 
(See  below.)^ 

Action  of  Gastric  Juice.  —  Most  proteid  substances  are  insoluble 
in  water.  They  belong  to  the  class  of  substances  known  as  ''  col- 
loids"  — substances  that  do  not  easily  pass  through  a  membrane 
by  osmosis.  Protein  is  changed  by  the  pepsin  of  the  gastric  fluid 
to  a  substance  readily  soluble.  After  protein  is  digested  it  is 
known  as  a  peptone.  Digestion  of  proteid  results  in  a  change 
of  a  colloid  substance  to  one  which  will  diffuse  readily  through  a 
membrane,  or  a  crystalloid.     Peptones  are  crystalloid  substances. 

Gastric  juice  acts  most  perfectly  at  the  temperature  of  the  normal  body. 
The  enzyme  pepsin  will  not  act  in  an  alkaline  medium;  boiling  or  freezing 
prevents  its  action  as  well,  A  slightly  acid  medium  is  necessary  for  proteid 
digestion  in  the  stomach. 

The  other  enzyme  of  gastric  juice,  called  rennin,  curdles  or  coagulates 
the  proteid  found  in  milk;  after  the  milk  is  curdled,  then  the  enzyme, 
pepsin,  is  able  to  act  upon  it  and  change  it  to  a  soluble  crystalloid  substance. 

The  hydrochloric  acid  found  in  the  gastric  juice  acts  upon  lime  and 
some  other  salts  taken  into  the  stomach  with  food. 

Experiment.  —  Add,  drop  by  drop,  very  dilute  hydrochloric  acid  to  a 
test  tube  containing  limewater.  Notice  the  change  that  takes  place.  By 
this  means  lime  is  changed  from  an  insoluble  to  a  soluble  form  and  can  be 
absorbed  into  the  blood,  to  be  later  used  in  the  building  of  bone. 

Movement  of  Walls  of  Stomach.  —  The  stomach  walls,  provided  with 
three  layers  of  muscle  which  run  in  an  oblique,  circular,  and  longitudinal 
direction  (taken  from  the  inside  outward),  are  well  fitted  for  the  constant 
churning  of  the  food  in  that  organ.  Here,  as  elsewhere  in  the  digestive 
tract,  the  muscles  are  involuntary,  muscular  action  being  under  the  control 
of  the  so-called  sympathetic  nervous  system.  Food  material  in  the  stomach 
makes  several  complete  circuits  during  the  process  of  digestion  in  that 
organ.  While  this  is  taking  place,  the  gastric  juice  acts  upon  proteins, 
softening  them,  while  the  constant  churning  movement  tends  to  separate 
the  bits  of  food  into  finer  particles.  Finally,  some  of  the  partly  digested 
food  is  allowed  to  pass  in  small  amounts  through  the  pyloric  valve,  into 
the  small  intestines.  This  is  done  by  the  expansion  of  the  ringlike  muscles 
of  the  pylorus. 

^  The  food  test  for  proteid  already  given  (nitric  acid  followed  by  ammonium 
hydrate)  is  known  as  the  xanthoproteic. 

Another  test  is  made  in  the  following  manner :  Place  in  a  test  tube  containing 
proteid  some  concentrated  caustic  soda  solution.  To  this  add,  drop  by  drop,  a  little 
weak  copper  sulphate  solution.  Note  the  resulting  color  (violet).  Heat  the  material 
and  the  color  deepens. 

If  the  proteid  has  been  digested  to  peptone  the  above  test  will  show  a  rose  pink. 
This  test,  known  as  the  biuret  test,  is  used  for  the  detection  of  peptones. 

hunter's  BIOL.  —  22 


338  HUMAN   PHYSIOLOGY 

Absorption  in  Stomach.  —  Fluids  leave  the  stomach  more  rapidly 
than  do  solids,  milk,  for  example,  taking  about  two  hours  to  digest, 
while  a  meal  of  meat  and  vegetables  will  not  leave  the  stomach 
for  three  to  four  hours.  It  is  not  thought  that  any  great  amount 
of  absorption  of  digested  food  occurs  through  the  wall  of  the 
stomach.  As  soon  as  food  reaches  the  small  intestine,  however, 
sugars  and  peptones  are  slowly  absorbed,  and  pass  into  the  blood. 

The  Intestine  and  Glands  connected  with  it.  Laboratory  Work  on  the  Frog} 
—  The  liver  is  the  most  prominent  structure  found  in  the  body  cavity. 
Note  its  position,  its  red  color,  the  number  of  lobes  into  which  it  is  divided. 
If  the  liver  be  pushed  to  one  side,  the  small  intestine  is  found  to  occupy  part 
of  the  remaining  space  in  the  body  cavity.  Between  the  stomach  and  a 
coil  of  the  small  intestine  lies  a  pinkish  gland,  the  'pancreas.  The  duct 
or  tube  which  carries  its  secretion  empties,  together  with  the  bile  duct  from 
the  liver,  into  the  small  intestine,  a  short  distance  posterior  to  where  the 
latter  leaves  the  stomach.  Find  the  greenish  gall  bladder  which  holds  the 
secretion  of  the  liver,  the  bile.  Try  to  trace  the  course  of  the  bile  duct  to 
the  small  intestine.  Notice  the  abrupt  change  in  the  diameter  of  the  food 
tube  near  its  posterior  end  where  it  forms  the  large  intestine;  the  latter 
empties  into  a  space  called  the  cloaca.  This  forms  a  common  outlet  for 
the  food  tube,  kidneys,  and  reproductive  organs. 

Position  and  Structure  of  the  Pancreas.  —  In  man,  the  pancreas 
occupies  the  same  relative  position  that  it  does  in  the  frog.  The  gland  is  a 
rather  diffuse  structure;  its  duct  empties  in  a  common  opening  with  the 
bile  duct,  a  short  distance  below  the  pylorus.  In  internal  structure,  the 
pancreas  resembles  the  salivary  glands.  The  fluid,  as  we  shall  see,  has  some 
functions  possessed  by  the  saliva. 

The  following  experiments  may  be  performed  to  illustrate  the  process  of 
digestion  by  pancreatic  fluid.  The  several  enzymes  of  pancreatic  fluid  are 
sold  in  a  powdered  form  as  a  substance  called  pancreatin.^  An  artificial 
pancreatic  fluid  may  be  prepared  by  adding  to  some  pancreatin  enough 
water  to  dissolve  it.  To  show  saponification  of  fats  add  ten  volumes  of  1 .5 
per  cent  sodium  carbonate. 

Experiments  to  show  the  Properties  of  Pancreatic  Fluid.  —  Prepare  (1)  test 
tube  containing  starch  and  artificial  pancreatic  fluid;  (2)  test  tube  con- 
taining proteid  and  artificial  pancreatic  fluid;  (3)  test  tube  containing  oil 
and  artificial  pancreatic  fluid  4-  ten  volumes  of  1 .5  per  cent  sodium  carbonate ; 
(4)  test  tube  containing  oil  and  water.  Place  tubes  1  and  2  in  a  pan  con- 
taining warm  water.  Leave  at  a  temperature  of  98°  Fahrenheit,  if  possible, 
for  twelve  hours.  Then  test  No.  1  with  Fehling's  solution;  No.  2  for  pep- 
tone with  the  biuret  test.  Test  the  contents  of  tube  No.  1  or  No.  2  with 
red  litmus  paper.  What  reaction  do  j'-ou  obtain?  Shake  up  No.  3  and 
No.  4  an  equal  number  of  times;  compare  the  color  and  appearance  of  the 
two  tubes  one  minute  after  shaking.     Note  that  the  milky  condition  existing 

'  In  the  female  frog  it  will  be  necessary  to  remove  the  ovary,  filled  with  tiny  black 
and  white  eggs,  and  the  oviducts,  twisted  tubes  through  which  the  eggs  are  passed 
to  the  outside  of  the  body,  before  working  on  the  rest  of  the  digestive  tract. 

2  This  substance  must  be  bought  from  a  reliable  firm,  as  it  is  frequently  adulterated. 


DIGESTION  AND  ABSORPTION 


339 


in  No.  3  after  shaking  continues  for  a  longer  period  than  the  same  condition 
in  No.  4.  Examine,  under  the  compound  microscope,  a  drop  of  the  fluid 
taken  from  tube  No.  3.  Notice  the  fluid  appears  to  contain  thousands 
of  tiny  droplets  of  fat  which  float  in  the  water  surrounding  them.  Such 
a  mass  of  finely  separated  particles  of  oil  and  water  is  called  an  emulsion. 

Functions  of  Pancreatic  Fluid.  —  From  these  experiments  we  see  that 
pancreatic  fluid  is  alkaline  in  its  reaction.  It  has  the  power,  by  means  of 
an  enzyme  called  amolypsin,  to  change  starches  to  sugars.  A  second  enzyme, 
called  trypsin,  changes  proteids  to  peptones.  Oils  and  fats,  with  the  aid 
of  a  third  enzyme  (lipase)  are  emulsified  and  in  part  changed  to  soap. 
It  is  estimated  that  half  an  ounce  of  soap  is  formed  daily  in  the  small 
intestine  by  this  means.     In  such  a  form  fats  are  enabled  to  pass  through 


Appearance  of  milk  under  the  microscope,  showing  the  natural  grouping  of  the  fat  globules. 
In  the  circle  a  single  group  is  highly  magnified.  Milk  is  one  form  of  an  emulsion. 
(S.  M„  Babcock,  Wis.  Bui.  No.  61.) 


the  walls  of  the  intestine.  This  is,  then,  a  form  of  digestion.  The  pancre- 
atic fluid  is  thus  seen  to  play  a  very  important  part  in  digestion,  as  it  acts 
upon  all  three  nutrients,  starches,  proteids,  and  fats. 

Liver.  —  The  liver  is  the  largest  gland  in  the  body.  In  man,  it  hangs  just 
below  the  diaphragm,  a  little  to  the  right  side  of  the  body.  During  life,  its 
color  is  deep  red.  It  is  divided  into  three  lobes,  between  two  of  which  is 
found  the  gall  bladder,  a  thin-walled  sac  which  holds  the  bile,  a  secretion  of 
the  liver.  Bile  is  a  strongly  alkaline  fluid  of  greenish  color.  It  reaches  the 
intestine  through  a  common  opening  with  the  pancreatic  fluid.  Almost  one 
quart  of  bile  is  passed  daily  into  the  digestive  canal. 

Functions  of  Bile.  —  The  action  of  bile  on  foods  is  not  very  well  known. 
It  does  have  slight  action  in  emulsifying  fats.  It  is  slightly  antiseptic, 
and  is  thus  valuable  in  preventing  fermentation  within  the  intestine.  Its 
greatest  importance,  however,  is  the  peculiar  faculty  it  has  of  aiding  the 
passage  of  fats  through  the  walls  of  the  intestine. 


340 


HUMAN  PHYSIOLOGY 


Experiment.  —  Place  filter  paper  within  each  of  two  funnels.  In  one 
funnel,  wet  the  filter  paper  with  water.  In  the  second,  wet  the  paper  with 
ox  gall  dissolved  in  water  (equivalent  to  bile) .  Place  olive  oil  in  each  funnel. 
Through  which  filter  does  the  olive  oil  pass  with  greater  rapidity  ? 

Formation  of  Glycogen.  —  Another  important  function  of  the  liver 
(which  may  be  taken  up  in  connection  with  the  circulation  of  the  blood)  is 
the  formation  within  it  of  a  material  called  glycogen  or  animal  sugar.  The 
liver  is  supplied  by  blood  from  two  sources.  The  greater  amount  of  blood 
received  by  the  liver  comes  directly  from  the  walls  of  the  stomach  and  intes- 
tine to  this  organ.  This  blood  is  very  rich  in  food  materials,  and  from  it  the 
cells  of  the  liver  take  out  sugars  to  form  glycogen.  Glycogen  is  stored  in  the 
liver  until  such  a  time  as  a  food  is  needed  that  can  be  quickly  oxidized; 

then  the  glycogen  is  carried  off  by  the 
blood  to  the  tissue  which  requires  it  and 
there  used  for  this  purpose. 

The  Absorption  of  Digested  Food 
into  the  Blood. — The  object  of  diges- 
tion is  to  change  foods  from  an  in- 
soluble to  a  soluble  form.  This  has 
been  seen  in  the  study  of  the  action 
of  the  various  digestive  fluids  in  the 
body,  each  of  which  is  seen  to  aid  in 
dissolving  solid  foods,  changing  them 
to  a  fluid,  and,  in  case  of  the  bile, 
actually  assisting  them  to  pass  through 
the  wall  of  the  intestine  by  osmosis. 
A  YQvy  small  amount  of  digested  food 
may  be  absorbed  by  the  blood  in  the 
blood  vessels  of  the  walls  of  the  stom- 
ach. Most  of  the  absorption,  how- 
ever, takes  place  through  the  walls  of 
the  small  intestine.  Let  us  examine 
this  structure  somewhat  closely  to 
see  how  it  is  adapted  to  absorb  liquid 
food. 


A  much  magnified  section  through 
the  wall  of  the  small  intestine 
(after  Benda).  A,  B,  transverse 
folds  of  intestine  covered  with 
the  fingerlike  villi ;  note  the  very 
great  absorbing  surface  thus 
gained;  C,  connective  tissue; 
D,  E,  circular  and  longitudinally 
running  muscle  fibers. 


Structure  of  the  Small  Intestine. — . 
The  small  intestine  in  man  is  a  slender 
tube  nearly  twenty  feet  in  length  and  about  one  inch  in  diameter.  Its 
walls  contain  muscles  which,  by  a  series  of  slow  waves  of  contraction,  force 


DIGESTION   AND   ABSORPTION 


341 


the  fluid  food  gradually  toward  the  posterior  end  of  the  tube.  If  the 
chief  function  of  the  small  intestine  is  that  of  absorption,  we  must  look 
for  adaptations  which  increase  the  absorbing  surface  of  the  tube.  This  is 
gained  in  part  by  the  inner  surface  of  the  tube  being  thrown  into  transverse 
folds  which  not  only  retard  the  rapidity  with  which  food  passes  down  the 
intestine,  but  also  give  more  absorbing  surface.  But  far  more  important 
for  absorption  are  millions  of  little  projections  which  cover  the  inner  sur- 
face of  the  small  intestine.  So  numerous  are  these  projections  that  the 
whole  surface  presents  a  velvety  appearance.  Collectively,  these  structures 
are  called  the  villi  (singular  villus) .  They  form  the  chief  organs  of  absorp- 
tion in  the  intestine,  several  thousand  being 
distributed  over  every  square  inch  of  surface. 
Between  the  villi  are  found  the  openings  of 
many  small  tubelike  glands,  the  intestinal 
glands.  These  glands  manufacture  a  digest- 
ive fluid,  the  function  of  which  is  believed 
to  be  somewhat  like  that  of  the  pancreatic 
fluid. 

Internal  Structure  of  a  Villus.  —  The  in- 
ternal structure  of  a  villus  is  best  seen  in 
a  longitudinal  section.  We  find  the  outer 
wall  made  up  of  a  thin  layer  of  cells,  the 
epithelial  layer.  It  is  the  duty  of  these  cells 
to  absorb,  by  osmosis,  the  semifluid  food 
from  within  the  intestine.  Sugars  and  pep- 
tones are  passed  through  the  cells  to  a 
number  of  tiny  capillaries  or  blood  vessels 
found  immediately  under  the  epithelial 
layer.  From  here  they  pass  (through  what 
is  known  as  the  portal  circulation)  into  the 
liver,  where,  as  we  have  seen,  sugar  is  taken 
from  the  blood  and  stored  as  glycogen. 


Diagram  of  a  longitudinal  section 
through  a  villus;  a,  epithelium 
which  takes  up  food  and  trans- 
ports it  to  the  tubes  within; 
&,  an  artery;  c,  capillaries;  d,  a 
lacteal. 


Course  of  Food  after  Absorption.  —  From  the  liver,  this  food 
within  the  blood  is  sent  to  the  heart,  from  there  pumped  to  the 
lungs,  from  there  it  returns  to  the  heart  and  is  pumped  to  the 
tissues  of  the  body,  where  as  nitrogenous  food  it  may  build  proto- 
plasm or,  if  carbohydrate,  may  be  used  to  furnish  energy.  A  large 
amount  of  water  and  some  salts  are  absorbed  through  the  walls 
of  the  stomach  and  intestine  as  food  passes  on  its  course.  The 
fats,  in  the  form  of  an  emulsion,  are  also  taken  up  through  the 
cells  lining  the  villi  and  pass,  not  into  the  blood  vessels,  but  into 
a  space  which  occupies  part  of  the  interior  of  the  villus.     Each  of 


342  HUMAN  PHYSIOLOGY 

these  spaces  leads  into  a  system  of  thin-walled  vessels  which,  be- 
cause of  their  milky  appearance  after  their  absorption  of  fats,  are 
collectively  called  the  lacteals  (Lat.  lac  =  milk). 

Mesenteric  Glands.  — The  entire  digestive  tract  hangs  in  the  body  cavity 
within  a  double  fold  of  the.  mesentery  or  membrane  which  lines  the  body 
cavity.  In  this  double  fold  are  found,  besides  the  organs  of  the  digestive 
tract,  blood  vessels  leading  to  and  from  them,  nerves,  connective  tissue, 
and  fat,  numerous  small  collections  of  gland  cells  called  the  mesenteric 
glands.  These  glands  receive  the  fatty  contents  of  the  lacteals  and,  in 
some  way,  change  this  fat  so  that  it  mst,y  become  part  of  the  blood.  Even- 
tually, the  fats  reach  the  blood  through  the  thoracic  duct  of  the  lymphatic 
system  (which  we  shall  study  later).  Fats  reach  the  blood,  then,  without 
passing  through  the  liver  with  the  other  foods  absorbed  by  the  villi. 

Large  Intestine.  —  The  large  intestine  has  somewhat  the  same 
structure  as  the  small  intestine  except  that  the  diameter  is  much 
greater.  It  also  contains  no  villi  nor  transverse  folds  on  its  inner 
surface.  Considerable  absorption  of  food,  however,  takes  place 
through  its  walls  as  the  food  mass  is  slowly  pushed  along  by  the 
muscles  within  its  walls. 

Vermiform  Appendix.  —  At  the  point  where  the  small  intestine  T^idens 
to  form  the  large  intestine  a  baglike  pouch  is  formed.  From  one  side  ot  this 
pouch  is  given  off  a  small  tube  about  four  inches  long,  closed  at  the  lower 
end.  This  tube,  the  function  of  which  in  man  is  unknown,  is  called  the 
vermiform  appendix.  It  has  come  to  have  unpleasant  notoriety  in  late 
years,  as  the  site  of  serious  inflammation.  It  often  becomes  necessary  to 
remove  the  appendix  in  order  to  prevent  this  inflammation  spreading 
to  the  surrounding  tissues.  In  some  of  the  lower  vertebrates  (for  ex- 
ample, fishes),  the  vermiform  appendix  is  extremely  large,  and  appears 
to  be  used  as  an  organ  of  digestion  and  absorption.  In  man  it  has  become 
reduced  in  size  (perhaps  through  disuse)  so  that  it  is  a  mere  vestige  of  what 
it  is  in  lower  vertebrates. 

Hygienic  Habits  of  Eating;  the  Causes  and  Prevention  of  Dyspep- 
sia. —  From  the  contents  of  the  foregoing  chapter  it  is  evident  that 
the  object  of  the  process  of  digestion  is  to  break  up  solid  food 
so  that  it  may  be  absorbed  to  form  part  of  the  blood.  Any  hab- 
its we  may  form  of  thoroughly  chewing  our  food  will  evidently  aid 
in  this  process.  A  lump  of  white  of  egg  will  not  be  digested  by 
pepsin  in  the  experiment  just  performed;  minced  egg,  on  the  other 
hand,  is  quickly  changed  to  a  peptone.     Undoubtedly  much  of  the 


DIGESTION   AND  ABSORPTION 


343 


distress  known  as  dyspepsia  is  due  to  too  hasty  meals  with  con- 
sequent lack  of  proper  mastication  of  food.  Another  cause  is 
overeating.  It  is  a  good  rule  to  go  away  from  the  table  feeling 
hungry.  Eating  too  much  overtaxes  the  digestive  organs  and 
prevents  their  working  to  the  best  advantage.  Still  another 
cause  of  dyspepsia  is  eating  when  in  a  fatigued  condition.  It 
is  always  a  good  plan  to  rest  a  short  time  before  eating,  especially 
after  any  hard  manual  work.  Eating  between  meals  is  also 
condemned  by  physicians  because  it  calls  the  blood  to  the 
digestive  organs  at  a  time  when  it  should  be  in  other  parts 
of  the  body. 

Effect  of  Alcohol  on  Digestion.  —  It  is  a  well-known  fact  that 
alcohol  extracts  water  from  tissues  with  which  it  is  in  contact. 
This  fact  works  much  harm  to  the  interior  surface  of  the  food  tube, 
especially  the  walls  of  the  stomach,  which  in  the  case  of  a  hard 
drinker  are  likely  to  become  irritated  and  much  toughened.  In 
small  amounts  alcohol  is  believed  to  stimulate  the  secretion  of 
the  salivaric  and  gastric  glands,  and  thus  it  seems  to  aid  in  diges- 
tion.    It  is  doubtful,  however,  if  this  aid  is  real. 

The  following  results  of  experiments  on  dogs,  published  in  the 
American  Journal  of  Physiology,  Vol.  I,  Professor  Chittenden  gives 
as  "strictly  comparable,"  because  ''  they  were  carried  out  in  succes- 
sion on  the  same  day  " :  — 


Number  of  Experiment. 

^  lb.  meat  with  water. 

^  lb.  meat  vrith  dilute  alcohol. 

XVII    a  9  :  15  a.m. 

Digested  in  3  hours. 

XVII    ^3  :00  p.m. 

Digested  in  3  :  15  hours. 

XVIII  a  8  :  30  a.m. 

Digested  in  2  :  30  hours. 

XVIII  /3  2  :  10  P.M. 

Digested  in  3  :  00  hours. 

XIX      a  9  :  00  a.m. 

Digested  in  2  :  30  hours. 

XIX     /3  2  :  30  p.m. 

Digested  in  3  :  00  hours. 

XX       a  9:15  A.M. 

Digested  in  2  :  45  hours. 

XX       )8  2  :  .30  p.m. 

Digested  in  2  :  15  hours. 

VI         a  9: 15  A.M. 

Digested  in  3  :  45  hours. 

VI         j3  1  :  00  P.M. 

Digested  in  3  :  15  hours. 

Average     .    .    . 

2  :  42  hours. 

3  :  09  hours. 

XXIX.     THE   BLOOD 


Function  of  the  Blood.  —  We  have  seen  in  the  preceding  chapter 
that  the  chief  function  of  the  digestive  tract  is  to  change  foods 
to  such  form  that  they  can  be  absorbed  through  the  walls  of  the 
food  tube.      The  food,  after  it  has  passed  through  the  intestine 

walls,  ultimately  reaches  the 
blood  and  becomes,  as  we  shall 
see,  a  part  of  this  tissue.  By 
means  of  a  system  of  closed 
tubes,  this  fluid  tissue  circu- 
lates to  all  parts  of  the  body, 
depositing  its  burden  of  food 
at  the  places  where  it  is  most 
needed  and  where  it  will  be 
used,  either  in  the  rejDair  or 
building  of  tissues  or  in  the 
release  of  energy. 


■>w. 


Nucleated  blood  cells  of  a  frog,  as  seen  vmder 
the  compound  microscope;  a,  colorless 
corpuscles. 


Laboratory  Exercise.  —  Examine 
a  prepared  slide  of  the  blood  of  a 
frog.  Note  that  three  constituents 
are  found:  (1)  Ovoid  cells,  each 
containing  a  nucleus.  What  color 
do  these  bodies  have?  They  are  called  the  red  corpuscles.  (2)  Other 
colorless  corpuscles  of  irregular  form  may  be  seen.  What  can  you  say  of 
the  number  of  colorless  corpuscles  as  compared  with  the  red  corpuscles? 
Notice  that  the  colorless  corpuscles  have  the  power  to  change  their  shape. 
They  are  said  to  be  amoeboid.  Like  the  amoeba,  they  also  have  the  power 
to  take  up  particles  of  food  and  other  materials  and  ingest  them.  (3)  The 
colorless  fluid  in  which  the  corpuscles  float  is  known  as  the  plasma. 

Composition  of  Plasma.  —  The  plasma  of  blood  (when  chemically 
examined  in  man)  is  found  to  be  largely  (about  90  per  cent)  water. 
It  also  contains  a  considerable  amount  of  proteid,  some  sugar, 
fat,  and  mineral  material.  It  is,  then,  the  medium  which  holds  the 
fluid  food  (or  at  least  part  of  it)  that  has  been  absorbed  from  the 
food  within  the  intestine.     When  the  blood  returns  from  the  tis- 

344 


THE   BLOOD 


345 


sues  where  the  food  is  oxidized,  the  plasma  brings  back  with  it 
to  the  lungs  the  carbon  dioxide  liberated  from  the  tissues  of  the 
body  where  oxidation  has  taken  place.  Blood  returning  from  the 
tissues  of  the  body  has  from  45  to  50  cubic  centimeters  of  carbon 
dioxide  to  every  100  cubic  centimeters.  (See  Respiration,  page 
380.)  Some  waste  products,  to  be  spoken  of  later,  are  also  found 
in  the  plasma. 

Demonstration.  —  Get  some  fresh  beef  blood.  Let  it  stand  overnight  in  a 
jar.  In  the  morning  it  will  be  found  to  have  separated  into  two  parts,  a 
dark  red  clot  and  a  thin  straw-colored  liquid,  called  serum.  Serum  is  found 
to  be  made  up  of  about  90  per  cent  water,  8  to  9  per  cent  proteid,  and  from 
1  to  2  per  cent  sugars,  fats,  and  mineral  matter.  In  these  respects  it  rather 
closely  resembles  the  fluid  food  that  is  absorbed  from  the  intestines. 

Clotting  of  Blood.  —  Pour  another  jar  of  fresh  beef  blood  into  a  pan  and 
briskly  whip  it  with  a  bundle  of  little  rods  (or  with  an  egg  beater).  A 
stringy  substance  will  be  found  to  stick  to  the  rods.  This,  if  washed  care- 
fully, is  seen  to  be  almost  colorless.  Test  with  nitric  acid  and  ammonia. 
Note  the  deep  orange  color.     It  is  a  proteid  substance  called  fibrin. 

Blood  plasma,  then,  is  made  up  of  serum,  a  fluid  portion,  and 
fibrin,  which,  although  in  a  fluid  state  in  the  blood  vessels  within 
the  body,  coagulates  when  removed  from  the  body. 

It  is  this  coagulation  which  aids  in  the  formation  of  a  blood 
clot.  A  clot  is  simply  a  mass  of  fibrin  with  a  large  number  of 
corpuscles  tangled  within.  The  clotting  of  blood  is  of  great  physi- 
ological importance,  for  otherwise  we  might  bleed  to  death  from 
the  smallest  wound. 

In  blood  within  the  circulatory  system  of  the  body  the  fibrin 
is  held  in  a  fluid  state  called  fibrinogen.  It  is  believed  that  an 
enzyme,  acting  upon  this  fibrinogen, 
causes  the  change  to  take  place  in 
the  blood. 

The  Red  Blood  Corpuscle;  its 
Structure  and  Functions.  —  In  the 
blood  of  the  frog  we  have  seen  that 
the  red  corpuscle  is  a  true  cell  of  disk- 
like form.  The  red  corpuscle  of 
man,  however,  lacks  a  nucleus.  Its 
form  is  that  of  a  biconcave  disk. 
So  small  and  so  numerous  are  these 
corpuscles  that  over  five  million  are  found  in  a  drop  of  normal  blood. 


Human  blood  as  seen  under  the  com- 
pound microscope:  at  the  extreme 
right  is  a  colorless  corpuscle. 


346  HUMAN   PHYSIOLOGY 

The  color,  which  is  found  to  be  a  dirty  yellow  when  separate  corpus- 
cles are  viewed  under  the  microscope,  is  due  to  a  proteid  material 
called  haemoglobin.  Haemoglobin,  which  constitutes  about  35 
per  cent  of  the  corpuscle,  contains  a  large  amount  of  iron.  It  has 
the  power  of  uniting  very  readily  with  oxygen  whenever  that 
gas  is  abundant,  and  after  having  absorbed  it,  of  giving  it  up  to 
the  surrounding  media,  when  oxygen  is  there  present  in  smaller 
amounts  than  in  the  corpuscle.  This  function  of  carrying  oxygen  is 
the  one  important  function  of  the  red  corpuscles.  The  taking 
up  of  oxygen  is  accompanied  by  a  change  in  color  of  the  mass  of 
corpuscles  from  a  dull  red  to  a  bright  scarlet. 

Length  of  Life  of  Red  Corpuscles.  —  It  is  difficult  to  say  just 
how  long  the  red  corpuscles  live  in  the  body.  We  know,  how- 
ever, that  large  numbers  are  destroyed  every  day. 

The  coloring  matter  of  the  bile,  and  possibly  other  body  excre- 
tions, is  due  to  the  color  obtained  from  the  worn-out  blood  cor- 
puscles. To  make  up  for  the  loss  of  the  red  corpuscles,  new  ones 
are  manufactured  in  the  red  marrow  of  bone.  The  red  marrow 
cells  are  in  a  continual  state  of  division,  forming  new  red  corpuscles 
which  at  first  are  nucleated  cells.  These  later  lose  their  nuclei 
and  become  disk-shaped. 

The  Colorless  Corpuscle ;  Structure  and  Functions.  —  A  colorless 
corpuscle  is  a  cell  irregular  in  outline,  the  shape  of  which  is  con- 
stantly changing.  These  corpuscles  are  somewhat  larger  than  the 
red  corpuscles  but  less  numerous,  there  being  about  one  colorless 
corpuscle  to  every  three  hundred  red  ones.  They  seem  to  have 
the  power  of  movement,  for  they  are  found  not  only  inside  blood 
vessels,  but  outside  the  blood  tubes,  showing  that  they  have  worked 
their  way  between  the  cells  that  form  the  walls  of  the  blood 
vessels. 

A  Russian  zoologist,  Metchnikoff,  after  studying  a  number  of 
simple  animals,  such  as  medusse  and  sponges,  found  that  in  such 
animals  some  of  the  cells  lining  the  inside  of  the  food  cavity  take 
up  or  engulf  minute  bits  of  food.  Later,  this  food  is  changed 
into  the  protoplasm  of  the  cell.  Metchnikoff  believed  that  the 
colorless  corpuscles  of  the  blood  have  somewhat  the  same 
function.     This  he  later  proved  to  be  true.     Like  the  amoeba. 


THE   BLOOD 


347 


they  feed  by  engulfing  their  prey.  This  fact  has  a  very  important 
bearing  on  the  relation  of  colorless  corpuscles  to  certain  diseases 
caused  by  bacteria  within  the  body.  If,  for  example,  a  cut  be- 
comes infected  by  bacteria,  inflammation  may  set  in.  The  bacteria 
form  a  poison  known  as  a  toxin,  which  causes  this  inflammation  in 
their  immediate  neighborhood.  Colorless  corpuscles  at  once  sur- 
round the  spot  and  attack  the  bacteria.  If  the  bacteria  are  few 
in  number,  they  are  quickly  eaten  by  the  colorless  corpuscles, 
which  are  known  as  'phagocytes.     If  bacteria  are  present  in  great 


Diagram  showing  how  colorless  corpuscles  pass  between  the  cells  that  form  the  walls  of 
the  capillaries;  1,2,  3,  4<  different  stages.    Hall. 


quantities,  they  may  prevail  and  kill  the  phagocytes  by  poison- 
ing them.  The  dead  bodies  of  the  phagocytes  thus  killed  are 
seen  in  the  pus,  or  matter  which  accumulates  in  infected  wounds. 
In  such  an  event,  we  must  come  to  the  aid  of  the  colorless 
corpuscle  by  washing  the  wound  with  some  antiseptic,  as  weak 
carbolic  acid  or  hydrogen  peroxide. 

Number  and  Manufacture  of  Colorless  Corpuscles. — The  number 
of  colorless  corpuscles,  although  normally  about  17,000  to  a  drop  of  blood, 
may  vary,  especially  in  certain  diseases.  They  are  formed  in  large  numbeis 
within  the  lymph  glands  (collections  of  cells  which  are  found  here  and  there 
along  the  course  of  the  lymph  vessels).  The  spleen,  a  gland,  and  the 
marrow  of  bone  are  also  believed  to  manufacture  colorless  corpuscles. 


348  HUMAN  PHYSIOLOGY 

The  Amount  of  Blood  and  its  Distribution.  —  Protoplasm  of  the 
body,  as  we  know,  is  composed  largely  of  water.  The  blood 
forms,  by  weight,  about  one  thirteenth  of  the  body.  Its  distri- 
bution varies  somewhat  according  to  the  position  assumed  by  the 
body,  and  the  amount  of  undigested  food  in  the  stomach  and  in- 
testines. Normally,  about  one  half  of  the  blood  of  the  body  is 
found  in  or  near  the  organs  lying  in  the  body  cavity,  about  one 
fourth  in  the  muscles,  and  the  rest  in  the  heart,  lungs,  large 
arteries,  and  veins. 

Blood  Temperature.  —  The  temperature  of  blood  in  the  human 
body  is  normally  about  98.5°  Fahrenheit,  although  the  tempera- 
ture drops  almost  two  degrees  after  we  have  gone  to  sleep  at  night. 
It  is  highest  about  5  p.m.  and  lowest  about  4  a.m.  Any  consider- 
able variation  in  the  temperature  of  the  blood  means  death.  In 
fevers,  the  temperature  of  the  body  sometimes  rises  to  107°;  but 
unless  this  temperature  is  soon  reduced,  death  follows.  Any 
considerable  drop  in  temperature  below  the  normal  also  would 
mean  death.  Bodily  temperature,  as  we  know,  results  from 
the  oxidation  of  food ;  within  the  cells  of  the  tissues  in  all  parts 
of  the  body,  but  especially  those  of  the  muscles. 

Cold-blooded  Animals.  —  In  lower  animals  which  are  called  cold 
blooded,  the  blood  has  no  fixed  temperature,  but  varies  with  the  tempera- 
ture of  the  medium  in  which  the  animal  lives.  Frogs,  in  the  summer, 
may  sit  for  hours  in  water  with  a  temperature  of  almost  100°.  In  winter, 
they  often  endure  freezing  so  that  the  blood  and  lymph  within  the  spaces 
under  the  loose  skin  are  frozen  into  ice  crystals.  Such  frogs,  if  thawed 
out  carefully,  will  live.  This  change  in  body  temperature  is  evidently 
an  adaptation  to  the  mode  of  life. 

Necessity  of  Good  Food,  Fresh  Air,  and  Sleep.  —  Inasmuch  as  the 
fluid  part  of  the  blood  receives  its  nourishment  directly  from  the 
foods  which  are  taken  into  the  body,  it  follows  that  if  food  materials 
contain  an  ill-balanced  proportion  of  nutrients,  the  blood  and  the 
body  may  suffer.  Proteid  must  be  taken  into  the  blood  at  all 
times,  for  without  it,  no  protoplasm  can  be  formed.  More  carbo- 
hydrates and  fats  are  needed  in  winter.  Why?  The  red  cor- 
puscles, having  the  important  function  of  carrying  oxygen,  must 
be  kept  in  healthy  condition.     To  do  this,  plenty  of  fresh  air  is 


THE   BLOOD  349 

essential.  Sleep  also  seems  to  be  a  necessary  factor  in  the  health 
of  the  red  corpuscle.  Many  are  familiar  with  the  pale  face 
which  comes  from  sleeplessness  and  overwork  in  poorly  ventilated 
rooms.  Moderate  exercise  is  another  important  factor.  The 
disease  called  anaemia,  which  means  a  lack  of  red  corpuscles  in 
the  blood,  is  too  often  brought  about  by  sedentary  habits  and 
lack  of  sleep  and  air.  Tonics  containing  iron  are  given  in  such 
cases  so  as  to  supply  the  lacking  element  to  the  haemoglobin  of  the 
red  corpuscle. 


XXX.    CIRCULATION 


Cat.  A. 


P.  A. 


The  Organs  of  Circulation  in  the  Frog.  —  In  a  frog  that  has  been  recently 
killed  the  organs  of  circulation  may  be  made  out  in  part.  It  is  best,  how- 
ever, to  have  a  specimen  in  which  the  blood  vessels  have  been  injected  with 
some  semifluid  mass  (made  of  gelatine  or   starch    colored  with  carmine 

or  other  bright  coloring  material).  Two  speci- 
mens should  be  used  to  demonstrate  the  organs 
of  circulation,  one  for  the  veins,  the  other  for  the 
arteries.  In  a  specimen  killed  by  chloroform- 
ing find  the  nearly  triangular-shaped  heart.  It 
is  seen  to  be  composed  of  two  distinct  parts, 
a  light-colored  area,  the  ventricle,  and  a  broader 
portion,  which  is  darker  in  color.  This  latter 
area  is  made  up  of  the  two  auricles.  Compare 
the  two  areas  of  the  heart  in  position.  The 
auricles,  according  to  their  position,  are  called 
respectively  the  right  and  left  auricles. 

The  arterial  system  of  the  frog  may  be  said  to 
include  all  blood  vessels  which  carry  blood  away 
from  the  heart.  The  heart  is  only  imperfectly 
divided  into  a  right  and  a  left  heart,  there  being 
only  one  ventricle,  with  an  imperfect  partition 
wall  extending  in  an  anterior-posterior  direc- 
tion. Blood  leaves  the  heart  to  pass  to  the 
lungs  by  a  vessel  (shown  in  the  diagram),  known 
as  the  pulmo-cutaneous  trunk,  because  it  carries 
blood  to  the  skin  and  lungs.  Over  the  ventral 
surface  of  the  heart  is  found  a  large  common 
trunk,  the  conus.  This  divides  into  two  branches 
while  still  over  the  heart,  and  then  each  branch 
splits  into  three  large  arteries,  the  carotid,  sys- 
temic, and  pulmo-cutaneous  appearing  from  the 
midline  as  we  go  outwards.  Trace  the  course 
of  the  carotid  artery;  it  supplies  the  head  and 
neck  with  arterial  blood.  The  systemic  arteries 
are  the  most  important  in  the  body.  Trace  one 
backward  to  where  it  unites  with  its  neighbor 
on  the  opposite  side  of  the  body  to  form  the 
dorsal  aorta,  the  great  main  trunk  supplying 
the  organs  of  the  body  cavity  and  the  muscles 
of  the  body  and  legs.  Find  the  branches  passing  to  the  stomach,  intestine, 
liver,  and  other  organs  held  in  the  mesentery.  Farther  back,  arteries  may 
be  found  that  pass  to  the  kidneys  and  genital  organs.  The  aorta  divides 
to  form  two  large  trunks,  the  iliac  arteries,  that  supply  the  muscles  of  the 
hind  legs.  Make  a  drawing  to  show  the  principal  arteries  and  their  con- 
nection with  the  heart  of  the  frog. 

The  system  of  blood  vessels  which  return  blood  from  the  various  organs 
of  the  body  to  the  heart  is  known  collectively  as  the  venous  system  or  veins 

350 


Arterial  system  of  the  frog; 
Cat.  A.,  carotid  artery; 
D.A.,  dorsal  aorta; 
D.T.A.,  artery  to  diges- 
tive tract;  IL.,  iliac  artery; 
L.,  lungs;  K.,  kidney; 
P.A.,  pulmonary  artery; 
R.A.,  renal  artery;  V.H., 
ventricle  of  heart.  (After 
Parker  and  Haswell.) 


CIRCULATION 


351 


In  the  frog  some  of  these  blood  vessels  are  somewhat  difficult  to  find; 
otners  may  easily  be  seen.  One  which  collects  blood  from  the  skin  and 
muscles  near  the  ventral  surface  of  the  body, 
but  chiefly  from  the  hind  legs,  is  called  the 
abdominal  vein.  It  may  be  seen  near  the 
surface,  on  the  ventral  midline  of  the  body,  as 
we  open  the  frog  from  the  ventral  side.  This 
vein  turns  inward  at  a  point  nearly  between 
the  fore  limbs,  divides  into  two  branches, 
and  enters  the  liver.  Just  before  it  reaches  the 
liver,  another  vein,  bringing  blood  from  the 
digestive  tract,  joins  with  it.  The  rest  of 
the  blood  from  the  hind  legs  has  to  pass 
through  what  is  known  as  the  renal  portal 
system  of  circulation,  the  veins  of  which  send 
the  blood  through  the  kidney,  and  thence, 
by  a  large  single  vein  (the  postcaval  vein)  to 
a  thin-walled  sac  on  the  dorsal  side  of  the 
heart.  This  sac,  known  as  the  sinus  venosus, 
receives  the  blood  from  the  veins  and  emp- 
ties it  into  the  heart.  Immediately  before 
reaching  the  sinus,  the  blood  from  the  liver 
(the  so-called  portal  circulation)  joins  with 
the  postcaval  vein.  It  is  seen  in  the  portal 
circulation  that  part  of  the  blood  of  the 
body  passes  through  the  liver  before  reaching 
the  heart.  Blood  from  the  head  region  is 
returned  to  the  heart  by  two  large  precaval 
veins.  The  blood  from  the  fore  limbs  also 
takes  this  course. 


^2cV.' 


Venous  system  of  the  frog;  a.b.d., 
abdominal  vein;  f.r.,  femoral 
vein;  H,  heart;  L,  lungs;  K, 
kidney;  LIV.,  liver;  P. F.,  pul- 
monary vein;  Pr.  CV.V.,  pre- 
caval vein;  R.,  R.,  renal  veins; 
SV,  sinus  venosus;  Sc.V.,  sci- 
atic veins.  (After  Parker  and 
Haswell.) 


Circulation  of  the  Blood  in  Man.  —  As  in  the  frog  and  other 
vertebrate  animals,  the  organs  of  circulation  are  the  heart  and  blood 
vessels.  These  blood  vessels  are  called  arteries  when  they  carr}^ 
blood  away  from  the  heart,  veins  when  they  bring  blood  back  to 
the  heart,  and  capillaries  when  they  connect  the  arteries  with  the 
veins.  Except  in  the  spleen,  where  the  blood  capillaries  are  open, 
blood  flowing  between  and  around  the  cells,  the  organs  of  circu- 
lation form  a  system  of  closed  tubes  through  which  the  blood  flows 
in  a  continuous  stream. 

The  Heart;  Position,  Size,  Protection. — The  heart  is  a  cone- 
shaped  muscular  organ  about  the  size  of  a  man's  fist.  It  is  located 
immediately  above  the  diaphragm,  and  lies  so  that  the  muscular 
apex,  which  points  downward,  moves  in  beating  or  contracting 
against  the  fifth  and  sixth  ribs,  just  a  little  to  the  left  of  the  mid- 
line of  the  body.  This  fact  gives  rise  to  the  notion  that  the  heart 
is  on  the  left  side  of  the  body.     The  heart  is  surrounded  by  a  loose 


352 


HUMAN   PHYSIOLOGY 


membranous  bag  called  the  pericardium.  The  inner  lining  of  the 
pericardium  secretes  a  fluid  in  which  the  heart  lies.  This  fluid 
prevents  any  friction  which  otherwise  might  arise  from  the  con- 
stant movement  of  the  heart  against  the  surrounding  tissues. 
When,  for  any  reason,  the  pericardial  fluid  is  not  secreted;  inflam- 
mation arises  in  that  region. 

Internal  Structure  of  Heart.  —  If  we  should  cut  open  the  heart  of 
an  ox,  down  the  midline,  we  could  divide  it  into  two  parts,  each 

of  which  would  have  no  internal  connec- 
tion with  the  other.  Each  side  of  the 
heart  is  found  to  be  distinct  and  to  be 
made  up  of  a  thin-walled  portion  with  a 
rather  large  internal  cavity,  the  auricle, 
and  a  smaller  portion  with  heavy  mus- 
cular walls,  the  ventricle.  The  auricles 
occupy  the  base  of  the  cone-shaped  heart; 
the  ventricles,  the  apex.  The  auricle  of 
the  right  side  communicates  with  the  ven- 
tricle of  that  side.  In  the  same  manner 
the  auricle  of  the  left  side  is  connected 
with  the  ventricle  on  the  left  side.  Com- 
munication between  auricles  and  ventri- 
cles is  guarded  by  little  flaps  of  muscle 
called  valves.  The  auricles  receive  blood 
from  the  veins.  The  ventricles  pump  the 
blood  into  the  arteries.  From  each  ven- 
tricle, large  arteries  leave  the  heart;  that 
of  the  left  side  is  called  the  aorta. 
Through  the  aorta,  blood  passes  to  all 
parts  of  the  body.  On  the  right  side,  the 
pulmonary  artery  carries  blood  to  the 
lungs.  The  openings  to  these  arteries  are 
guarded  by  three  halfmoon-shaped  flaps,  which  open  so  as  to  allow 
blood  to  pass  away  from  the  ventricle,  but  not  to  go  back  into  it 
when  the  muscles  relax.  The  heart  is  constructed  on  the  same 
plan  as  a  pump,  the  valves  preventing  the  reflux  of  blood  into  the 
auricle  after  it  is  forced  out  of  the  ventricle. 


Diagrams  illustrating  the  force- 
pump  action  of  the  valves 
of  the  heart;  A,  during  the 
filling  of  the  right  ventricle; 
B,  during  the  contraction  of 
the  ventricle. 


CIRCULATION  353 

The  Heart  in  Action.  —  In  a  quiet  room,  the  pulsation  of  the  heart 
may  be  distinctly  heard.  A  long  sound,  lub,  is  followed  by  a  short 
one,  dub.  The  first  sound  is  caused  by  the  contraction  of  the 
muscles  of  the  heart;  the  latter  sound  by  the  closing  of  the  valves 
in  the  heart.  The  action  of  the  heart  is  somewhat  like  that  occur- 
ring when  we  squeeze  water  through  a  rubber  bulb.  Blood  enters 
the  auricles  from  the  veins  because  the  muscles  of  that  part  of  the 
heart  relax;  this  allows  the  space  within  the  auricles  to  fill.  Al- 
most immediately  the  muscles  of  the  ventricles  relax,  thus  allow- 
ing blood  to  pass  into  the  chambers  within  the  ventricles.  Then, 
after  a  short  pause,  during  which  time  the  muscles  of  the  heart  are 
resting,  a  w^ave  of  muscular  contraction  begins  in  the  auricles  and 
ends  in  the  ventricles,  with  a  sudden  forceful  contraction  which 
forces  the  blood  out  into  the  arteries. 
This  contraction  of  the  heart  is  known 
as  a  systole.  The  extension  of  the  muscles, 
to  allow  the  auricles  and  ventricles  to  fill, 
is  called  a  diastole.  Blood  is  kept  on  its 
course  by  the  valves,  which  act  in  the  same 
manner  as  do  the  valves  in  a  pump,  thus 
forcing  the  blood  to  pass  into  the  arteries     ^  .•      r       . 

^  ,     ^  Transverse  section  or  an  artery, 

upon  the  contraction  of  ventricle  walls.  showing  muscular  walls. 

The  Work  of  the  Heart. — The  work  performed  by  the  heart  is  consid- 
erable. The  two  ventricles,  at  each  pulsation,  expel  about  a  cup  and  a  half 
of  blood  into  the  arteries  of  the  body.  The  average  rate  of  the  heart  beat  is 
about  seventy  to  the  minute,  so  that  the  work  of  the  ventricles,  in  a  single 
day,  is  estimated  to  release  enough  energy  to  lift  193  tons  one  foot  from  the 
ground.  The  heart  is  estimated  to  do  as  much  work  in  a  single  day  as  a 
moderately  heavy  man  would  perform  in  climbing  a  mountain  3600  feet 
in  height. 

Demonstration.  The  Circulation  of  Blood  in  a  Frog's  Foot.  —  Bore  a 
half  inch  hole  in  one  end  of  a  shingle.  Wrap  a  live  frog  in  wet  flannel  or 
absorbent  cotton,  and  bind  it,  by  means  of  elastic  bands,  upon  the  board 
so  that  the  web  of  the  foot  is  stretched  in  a  horizontal  position  over  the  hole. 
Keep  the  web  of  the  foot  wet.  Cover  it  with  a  large  coverslip.  Place  it 
on  the  stage  of  a  compound  microscope,  focus  with  low  and  then  with  the 
high  power.  A  network  of  blood  vessels  will  be  seen  which  maj^  be  partially 
obscured  by  numerous  pigment  cells  (dark-colored  cells  of  irregular  shape). 
The  blood  vessels  may  easily  be  recognized  by  the  fluid  contents,  the  ovoid 
corpuscles  floating  in  the  transparent  plasma.  Note  that  in  some  of  the 
blood  tubes  the  blood  moves  in  regular  spurts.      These  are  the  arteries. 

hunter's  BIOL.  —  23 


354 


HUMAN   PHYSIOLOGY 


Trace  the  artery  until  it  breaks  out  into  very  tiny  tubes,  the  capillaries. 
Notice  that  in  the  capillaries  the  diameter  of  the  tube  is  little  more  than  that 
of  a  red  corpuscle.  Follow  the  capillaries  until  they  come  together  to  form 
a  vein.  What  difference  in  the  movement  of  the  blood  do  you  notice  in  the 
veins? 


Capillary  circulation  in  the  web  of  a  frog's  foot,  as  seen  imder  the  compound  microscope; 
a,  b,  small  veins;  d,  capillaries  in  which  the  oval  corpuscles  are  seen  to  follow  one  anothei 
in  single  series;  c,  pigment  cells  in  the  skin. 


jStructure  of  the  Arteries.  —  A  distinct  difference  in  structure 
exists  between  the  arteries  and  the  veins  in  the  human  body.  The 
arteries,  because  of  the  greater  strain  received  from  the  blood 
which  is  pumped  from  the  heart,  have  thicker  muscular  walls, 
and,  in  addition,  are  very  elastic. 

Cause  of  the  Pulse. — The  pulse,  which  can  easily  be  detected  by  press- 
ing the  large  artery  in  the  wrist  or  the  small  one  in  front  of  and  above  the 
external  ear,  is  caused  by  the  gushing  of  blood  through  the  arteries  after  each 
pulsation  of  the  heart.  In  the  earthworm,  we  found  that  certain  parts  of 
the  blood  vessels  take  up  the  work  of  pumping  the  blood.  These  vessels 
which  connect  the  dorsal  with  the  ventral  blood  vessels  are  called  hearts. 
Each  is  a  single  muscular  tube.  The  fish  has  such  a  heart.  In  the  higher 
vertebrates  the  heart  is  more  complex,  being  composed  of  two  such  muscu- 


CIRCULATION 


355 


lar  tubes,  side  by  side,  each  having  two  chambers  (auricle  and  ventricle). 
As  the  large  arteries  pass  away  from  the  heart,  the  diameter  of  each 
individual  artery  becomes  smaller.  At  the  very  end  of  their  course, 
these  arteries  are  so  small  as  to  be  almost  microscopic  in  size.  They  are 
very  numerous.  There  are  so  many  that  if  they  were  placed  together, 
side  by  side,  their  united  diameter  would  be  much  greater  than  the 
diameter  of  the  large  artery  (aorta)  which  passes  blood  from  the  left 
side  of  the  heart.  This  fact  is  of  very  great  importance,  for  the  force 
of  the  blood  as  it  gushes  through  the  arteries  becomes  very  much  less 
when  it  reaches  the  smaller  vessels.  This  gushing  movement  is  quite  lost 
when  the  capillaries  are  reached.  First,  because  there  is  so  much  more 
space  for  the  blood  to  fill;  secondly,  there  is  considerable  friction  caused 
by  the  very  tiny  diameter  of  the  capillaries. 

Capillary  NetworH 


Capillary  network,  showing  change  from  arterial  to  venous  blood. 


Capillaries. — The  capillaries  form  a  network  of  minute  tubes 
everywhere  in  the  body,  but  especially  near  the  surface  and  in  the 
lungs.  It  is  through  their  walls  that  the  food  and  oxygen  pass  to 
the  tissues,  and  carbon  dioxide  is  given  up  to  the  plasma.  They 
form  the  connection  that  completes  the  system  of  circulation  of 
blood  in  the  body. 

Function  and  Structure  of  the  Veins.  —  If  the  arteries  are  pipes 
which  supply  fluid  food  to  the  tissues,  then  the  veins  may  be 
likened  to  drain  pipes  which  carry  away  waste  material  from  the 
tissues.  Extremely  numerous  in  the  extremities  and  in  the  muscles 
and  among  other  tissues  of  the  body,  they,  like  the  branches  of  a 


356 


HUMAN   PHYSIOLOGY 


tree,  become  larger  and  unite  with  each  other  as  they  approach  the 
heart.  The  blood  supply  from  the  body  enters  the  right  heart 
(auricle)  by  two  large  vessels,  called,  respectively,  because  of  their 
position,  the  inferior  and  superior  vence  cavce. 

If  the  wall  of  a  vein  is  carefully  examined,  it  will  be  found  to 
be  not  so  thick  or  so  tough  as  an  arter}^  wall.     When  empty,  a 
vein  collapses;    the  wall  of  an  artery  holds  its  position.     If  you 
hold  your  hand  downward  for  a  little  time  and  then  examine  it, 
j^ou  will  find  that   the  veins,  which  are  relatively 
much   nearer  the   surface   than    are    the    arteries, 
appear  to  be  very  much  knotted.     This  appearance 
is  due  to  the  presence  of  tiny  valves  inside  the  veins. 
These  valves  open  in  the  direction  of  the  blood  cur- 
rent, but  would  close  if  the  direction  of  the  blood 
flow  should  be  reversed  (as  in  case  a  deep  cut  sev- 
ered a  vein).    As  the  pressure  of  blood  in  the  veins 
is  much  less  than  in  the  arteries,  these  valves  thus 
aid  in  keeping  the  flow  of  blood  in  the  veins  toward 
the  heart.  ' 

The  Course  of  the  Blood  in  the  Body.  —  Although 
the  two  sides  of  the  heart  are  separate  and  distinct 
from  each  other,  yet  ever}^  drop  of  blood  that  passes 
through  the  left  heart  likewise  passes  through  the 
right  heart.  There  are  two  distinct  systems  of  cir- 
culation in  the  body.  The  'pulmonary  circulation 
takes  the  blood  through  the  right  auricle  and  ven- 
tricle, to  the  lungs,  and  passes  it  back  to  the 
left  auricle.  This  is  a  relatively  short  circulation,  the  blood  re- 
ceiving in  the  lungs  its  supply  of  oxygen,  and  there  giving  up 
some  of  its  carbon  dioxide.  The  greater  circulation  is  known  as 
the  systemic  circulation;  in  this  system,  the  blood  leaves  the  left 
ventricle  through  the  great  dorsal  aorta.  A  large  part  of  the 
blood  passes  directly  to  the  muscles;  some  of  it  goes  to  the  ner- 
vous system,  kidneys,  skin,  and  other  organs  of  the  body.  It 
gives  up  its  supply  of  food  and  oxygen  in  these  tissues,  receives 
the  waste  products  of  oxidation  while  passing  through  the  capil- 
laries, and  returns  to  the  right  auricle  through  the  venae  cavse.    It 


Valves  in  a 
vein. 


CIRCULATION 


357 


requires  from  twenty  to  thirty  seconds  only  for  the  blood  to  make 
the  complete  circulation  from  the  ventricle  back  again  to  the 
starting     point.       This 

means  that   the  entire  0^'^^^^=^^^^^'^^ 

volume  of  blood  in  the 

human    body     passes 

three  or  four  thousand 

times  a  day  through  the 

various    organs   of    the 

body.^ 

Portal  Circulation. 
—  Some  of  the  blood,  on  its 
return  to  the  heart,  passes 
by  an  indirect  path  through 
the  spleen,  pancreas,  and 
other  organs  of  the  body 
cavity,  to  the  liver.  Here 
the  vein  which  carries  the 
blood  (called  the  portal 
vein)  breaks  up  into  capil- 
laries around  the  cells  of 
the  liver.  We  have  already 
learned  that  the  liver  is  a 
great  storehouse  of  animal 
sugar  called  glycogen.  This 
glycogen  is  a  food  that 
may  be  easily  oxidized  to 
release  energy,  and  is  stored 
for  that  purpose .  The  sugar 
that  becomes  glycogen  is 
carried  to  the  liver  directly 
from  the  walls  of  the  stom- 
ach and  intestine,  where  it 
has  been  absorbed  from  the 
food  there  contained.  From 

the  liver,  blood  passes  directly  to  the  right  auricle.  The  fortal  system, 
as  it  is  called,  is  the  only  part  of  the  circulation  where  the  blood  passes 
through  two  sets  of  capillaries. 

Changes  in  Blood  within  the  Body.  —  We  have  already  seen  that 
blood  loses  much  of  the  carbon  dioxide  it  has  taken  from  the  tissues, 

^  See  Hough  and  Sedgwick,  The  Human  Mechanism,  page  136. 


Diagram  of  the  course  of  the  blood  in  the  circulation. 


358 


HUMAN   PHYSIOLOGY 


replacing  it  with  oxygen.  This  is  accompanied  by  a  change  of  color 
from  purple  (in  blood  which  is  poor  in  oxygen)  to  that  of  bright 
red  (in  richly  oxygenated  blood).  Other  changes  take  place  in 
other  parts  of  the  body.  In  the  muscles  the  blood  gives  up  food 
and  oxygen,  receiving  carbon  dioxide  in  return.  In  the  liver,  the 
blood  gives  up  its  sugar.  In  glands,  it  gives  up  materials  used  by 
the  gland  cells  in  their  manufacture  of  secretions.  In  the  kidneys, 
it  loses  water  and  nitrogenous  wastes  (urea).  In  the  skin,  it  also 
loses  some  waste  materials  and  water. 

Function  of  Lymph.  —  Different  tissues  and  organs  of  the  body 
are  traversed  by  a  network  of  tubes  which  carry  the  blood.     Inside 

these  tubes  is  the  blood  proper, 
consisting  of  a  fluid  plasma, 
the  colorless  corpuscles,  and 
the  red  corpuscles.  Outside 
the  blood  tubes,  in  spaces  be- 
tween the  cells  which  form  tis- 
sues, is  found  another  fluid  very 
much  like  plasma  of  the  blood 
in  chemical  composition.  This 
is  the  lymph.  It  is,  in  fact,  a 
fluid  food  in  which  some  color- 
less amoeboid  corpuscles  are 
found.  Blood  gives  much  of  its  food  material  to  the  lymph.  This 
it  does  by  passing  it  through  the  walls  of  the  capillaries.  The 
food  is  in  turn  given  up  to  the  tissue  cells  which  are  bathed  by 
the  lymph. 

Some  of  the  amoeboid  corpuscles  from  the  blood  make  their  way 
between  the  cells  forming  the  walls  of  the  capillaries.  Lymph, 
then,  is  practically  blood-plasma  plus  some  colorless  corpuscles.  It 
acts  as  the  medium  of  exchange  between  the  blood  proper  and  the  cells 
in  the  tissues  of  the  body.  It  not  only  gives  food  to  the  cells  of 
the  body  but  also  takes  away  vv^aste  materials,  which  are  ulti- 
mately passed  out  of  the  body  by  means  of  the  skin  and  kidneys. 

Lymph  Vessels.  —  The  lymph  is  collected  from  the  various  tissues  of 
the  body  by  means  of  a  number  of  very  thin-walled  tubes,  which  are  at 
first  very  tiny,  but  after  repeated  connection  with  other  tubes  ultimately 


Diagram  showing  how  food  reaches  the  cells 
from  the  capillaries. 


CIRCULATION 


359 


unite  to  form  large  ducts.  These  lymph  ducts  are  provided,  like  the  veins, 
with  valves.  The  pressure  of  the  blood  within  the  blood  vessels  forces 
continually  more  plasma  into  the  lymph ;  thus  a  slow  current  is  maintained 
from  the  lymph  spaces  toward  the  veins.  On  its  course  the  lymph  passes 
through  many  collections  of  gland  cells,  the  hjmph  glands.  In  these  glands 
some  impurities  appear  to  be  removed  and  colorless  corpuscles  made. 
The  lymph  ultimately  passes  into  a  large 
tube,  the  thoracic  duct,  which  flows  up- 
ward near  the  ventral  side  of  the  spinal 
column,  and  empties  into  the  large  sub- 
clavian vein  in  the  left  side  of  the  neck. 
Another  smaller  lymph  duct  enters  the 
right  subclavian  vein. 

The  Lacteals.  —  We  have  already 
found  that  part  of  the  digested  food 
(chiefly  carbohydrates,  peptones,  salts, 
and  water)  is  absorbed  directly  into  the 
blood  through  the  walls  of  the  villi  and 
carried  to  the  liver.  Some  of  the  food, 
however,  especially  fats,  makes  its  way 
into  the  spaces  in  the  central  part  of  the 
villi,  and  from  there  into  other  loose 
spaces  between  the  tissues,  known  as  the 
lacteals.  The  lacteals  form  the  most 
direct  course  for  the  fats  to  reach  the 
blood.  The  lacteals  and  lymph  vessels  have  in  part  the  same  course.  It 
will  be  thus  seen  that  lymph  at  different  parts  of  its  course  would  have  a 
very  different  composition. 

The  Nervous  Control  of  the  Heart  and  Blood  Vessels. — Although 
the  muscles  of  the  heart  contract  and  relax  without  our  being  able  to  stop 
them  or  force  them  to  go  faster,  yet  in  cases  of  sudden  fright  or  after  a  sud- 
den blow,  the  heart  may  stop  beating  for  a  short  interval.  This  shows  that 
the  heart  is  under  the  control  of  the  nervous  system.  Two  sets  of  nerve 
fibers,  both  of  which  are  connected  with  the  central  nervous  system,  pass  to 
the  heart.  One  set  of  fibers  accelerates,  the  other  slows  or  inhibits,  the  heart 
beat.  The  arteries  and  veins  are  also  under  the  control  of  the  sympathetic 
nervous  system.  This  allows  of  a  change  in  the  diameter  of  the  blood 
vessels.  Thus,  blushing  is  due  to  a  sudden  rush  of  blood  to  the  surface  of 
the  body,  caused  by  an  expansion  of  the  blood  vessels  at  the  surface.  The 
blood  vessels  of  the  body  are  always  full  of  blood.  This  results  from  an 
automatic  regulation  of  the  diameter  of  the  blood  tubes  by  a  part  of  the 
nervous  system  called  the  vasomotor  nerves.  These. nerves  act  upon  the 
muscles  in  the  walls  of  the  blood  vessels.  In  this  way,  each  vessel  adapts 
itself  to  the  amount  of  blood  in  it  at  a  given  time.     After  a  hearty  meal, 


Lacteal  system  of  mammal ;  a,  descend- 
ing aorta,  or  principal  artery;  h, 
thoracic  duct;  c,  origin  of  lacteal 
vessels;  g,  in  the  walls  of  the  intes- 
tine, d',  e,  mesentery,  or  membrane 
attaching  the  intestine  to  walls  of 
the  body;  /,  lacteal,  or  mesenteric, 
glands. 


360  HUMAN   PHYSIOLOGY 

a  large  supply  of  blood  is  needed  in  the  walls  of  the  stomach  and  intestines 
At  this  time,  the  arteries  going  to  this  region  are  dilated  so  as  to  receive 
an  extra  supply.  When  the  brain  performs  hard  work,  blood  is  supplied 
in  the  same  manner  to  that  region.  Hence,  one  should  not  study  or  do 
mental  work  immediately  after  a  hearty  meal,  for  blood  will  be  drawn  away 
to  the  brain,  leaving  the  digestive  tract  with  an  insufficient  supply.  In- 
digestion may  follow  as  a  result. 

The  Effect  of  Exercise  on  the  Circulation.  —  It  is  a  fact  familiar  to 
all  that  the  heart  beats  more  violently  and  quickly  when  we  are  doing  hard 
work  than  when  we  are  resting.  Count  your  own  pulse  when  sitting  quietly, 
and  then  again  after  some  brisk  exercise  in  the  gymnasium.  Exercise 
in  moderation  is  of  undoubted  value,  because  it  sends  the  increased  amount 
of  blood  to  such  parts  of  the  body  where  increased  oxidation  has  been 
taking  place  as  the  result  of  the  exercise.  Exercise  also  affects  the  diameter 
of  the  blood  vessels  because  the  sympathetic  nervous  system  at  this  time 
causes  the  muscular  walls  of  the  arteries  to  relax.  Exercise  should  not  be 
attempted  immediately  after  eating.  This  causes  a  withdrawal  of  blood 
from  the  walls  of  glands  of  the  digestive  tract  to  the  muscles  of  the  body. 

Treatment  of  Cuts  and  Bruises.  —  Blood  which  oozes  slowly 
from  a  cut  will  usually  stop  flowing  by  the  natural  means  of  the 
formation  of  a  clot.  A  cut  or  bruise  should,  however,  be  washed 
in  a  weak  solution  of  carbolic  acid  or  some  other  antiseptic  in  order 
to  prevent  bacteria  from  obtaining  a  foothold  on  the  exposed  flesh. 
If  blood,  issuing  from  a  wound,  is  bright  red  in  color  and  gushes 
indistinct  pulsations,  then  we  know  that  an  artery  has  been  severed. 
To  prevent  the  flow  of  blood,  a  tight  bandage  must  be  tied  between 
the  cut  and  the  heart.  A  handkerchief  with  a  knot  placed  over 
the  artery  may  stop  bleeding  if  the  cut  is  on  one  of  the  limbs. 
If  this  does  not  serve,  then  insert  a  stick  in  the  handkerchief  and 
twist  it  so  as  to  make  the  pressure  around  the  limb  still  greater. 
Thus  we  may  close  the  artery  until  the  doctor  is  called,  who  may 
sew  up  the  injured  blood  vessel. 

The  Effect  of  Alcohol  on  the  Circulation.  —  Alcoholic  drinks 
affect  the  very  delicate  adjustment  of  the  nervous  centers  control- 
ling the  blood  vessels  and  heart.  Even  very  dilute  alcohol  acts 
upon  the  muscles  of  the  tiny  blood  vessels,  consequently,  more 
blood  is  allowed  to  enter  them,  and,  as  the  small  vessels  are  usually 
near  the  surface  of  the  body,  the  habitual  redness  seen  in  the  face 
of  hard  drinkers  is  the  ultimate  result. 


CIRCULATION  361 

"The  first  effect  of  diluted  alcohol  is  to  make  the  heart  beat 
faster.  This  fills  the  small  vessels  near  the  surface.  A  feeling  of 
warmth  is  produced  which  causes  the  drinker  to  feel  that  he  was 
warmed  by  the  drink.  This  feeling,  however,  soon  passes  away, 
and  is  succeeded  by  one  of  chilliness.  The  body  temperature,  at 
first  raised  by  the  rather  rapid  oxidation  of  the  alcohol,  is  soon 
lowered  by  the  increased  radiation  from  the  surface. 

"  Alcohol  in  the  stomach  is  rapidly  absorbed  and  passes  into  the 
blood  stream.  There  the  strong  affinity  of  alcohol  for  oxygen, 
which  leads  them  to  enter  very  rapidly  into  chemical  combination, 
causes  the  alcohol  to  appropriate  the  oxygen  of  the  red  corpuscles 
of  the  blood,  which,  as  we  have  seen,  are  the  great  oxygen  carriers 
in  the  body.  This  tends  to  impoverish  the  blood  and  render  it  less 
valuable  to  the  tissues. 

"  The  immediate  stimulation  to  the  heart's  action  soon  passes 
away  and,  like  other  muscles,  the  muscles  of  the  heart  lose  power 
and  contract  with  less  force  after  having  been  excited  by  alco- 
hol."—  Macy,  Physiology. 

Alcohol,  when  brought  to  act  directly  on  heart  muscle,  lessens 
the  force  of  the  beat.  It  may  even  cause  changes  in  the  tissues, 
which  eventually  result  in  the  breaking  of  the  walls  of  a  blood 
vessel  or  the  plugging  of  a  vessel  with  a  blood  clot.  This  condition 
may  cause  the  disease  known  as  apoplexy. 

Effects  of  Tobacco  upon  the  Circulation.  — '*  The  frequent  use  of 
cigars  or  cigarettes  by  the  young  seriously  affects  the  quality  of 
the  blood.  The  red  blood  corpuscles  are  not  fully  developed  and 
charged  with  their  normal  supply  of  life-giving  ox3^gen.  This 
causes  paleness  of  the  skin,  often  noticed  in  the  face  of  the  young 
smoker.  Palpitation  of  the  heart  is  also  a  common  result,  followed 
by  permanent  weakness,  so  that  the  whole  system  is  enfeebled, 
and  mental  vigor  is  impaired  as  well  as  physical  strength."  — 
Macy,  Physiology, 


XXXI.     MUSCLES 


Muscles  and  Movement.  —  We  are  all  aware  that  motion  in  any 
of  the  higher  animals  is  caused  by  the  action  of  the  muscles. 
These  contract  and  expand,  thus  giving  the  required  amount  of 

movement.  In  man  and  the  other  vertebrate 
animals  the  muscles  are  fastened  to  bones,  which, 
acting  as  levers,  give  wide  range  of  motion. 
Study  of  the  muscles  in  the  leg  of  a  frog  will 
help  us  to  a  better  understanding  of  the  subject. 

Study  of  the  Muscles  of  a  Frog.  —  (Material  pre- 
served in  70  per  cent  alcohol  or  4  per  cent  formol  is 
best  for  this  purpose.)  Remove  the  skin  from  the  leg 
of  a  frog  by  stripping  it  downward  as  you  would  take 
off  a  glove.  Notice  the  yellowish-white  muscles  which 
form  the  "meat"  of  the  frog's  leg.  Notice  that  they 
are  more  or  less  separated  into  bundles  each  of  which 
tapers  at  the  end.  I^ook  for  dark-colored  blood  vessels 
and  tiny  white  nerves  which  lead  into  the  bundle  of 
muscles.  The  wide  part  of  the  muscle  is  called  the  belly. 
The  glistening  white  part  which  attaches  the  muscle 
to  the  bone  is  called  the  tendon.  Notice  the  large 
muscle  forming  the  calf  of  the  leg  (the  gastrocnemius). 
Try  to  make  out  what  movements  are  performed  by 
means  of  this  muscle.  (Pull  it  and  note  the  resulting 
movements.) 


Arrangement    of    Voluntary   Muscles    in    the 


Muscles  of  the  left  leg 
of  the  frog;   b,  M. 

biceps;  g,  M.  gas-     Humau   Body.  —  Muscles  are  usually  placed   in 

trocnemius;  sw,  M,  .  " 

semimembrano-     pairs;  oue.  Called  the  exteusor,  serv^es  to  straighten 

sus;  <r.  M.  triceps.       ^^^  .^.^^.    ^^^  ^^^^^^  ^j^^  ^^^^^^  ^^^^^^  ^^^  j^-^^^ 

Try  to  find  examples  of  flexor  and  extensor  muscles  in  the  leg  of 
the  frog.  Locate,  by  means  of  feeling  the  muscles  when  expanded 
and  contracted,  the  extensors  and  flexors  in  your  own  arm. 
This  paired  arrangement  of  muscles  is  of  obvious  importance,  a 
flexor  muscle  balancing  the  action  of  an  extensor  on  the  other 
side  of  the  joint.  The  end  of  the  muscle  that  has  the  wider 
movement  in  a  contraction  is  called  the  insertion;    the  part  th^-t 

303 


MUSCLES 


363 


moves  least  is  the  origin.  Muscles  are  named  biceps  or  triceps 
(two-headed  or  three-headed,  depending  on  the  number  of  tendons 
found  at  the  origin) :  the  gastroc- 
nemius, already  referred  to,  is  a 
biceps  muscle;  the  large  muscle 
forming  the  front  part  of  the  thigh 
is  a  triceps  muscle. 

Microscopic  Structure  of  Vol- 
untary Muscle.  —  With  a  sharp  pair 
of  scissors  cut  through  the  belly  of  a 
muscle  at  right  angles  to  the  long  axis  ; 
examination  will  show  that  it  is  com- 
posed of  a  number  of  bundles  of  fibers. 
These  fibers  are  held  together  by  a 
sheath  of  connective  tissue  called  the 
perimysium  (Lat.  =  around  the  mus- 
cle). Each  of  these  bundles  may  be 
separated  into  smaller  ones.  If  we 
continue  this  so  as  to  separate  into  the 
smallest  possible  bits  that  can  be  seen 
with  the  naked  eye,  and  then  examine 
such  a  tiny  portion  under  the  com- 
pound microscope,  it  will  present  some- 
what the  appearance  of  the  figure. 
The  muscle  is  seen  to  be  made  up  of 
a  number  of  tiny  threads  which  lie 
side  by  side,  held  together  by  the  peri- 
mysium. Each  thread  consists  of  sev- 
eral muscle  fibers,  each  of  which  is 
inclosed  in  a  tiny  sheath.  A  single 
fiber  under  the  compound  microscope 
appears  to  have  alternate  light  and 
dark  bands  running  at  right  angles  to 
its  long  axis.  This  gives  the  bundle  of 
fibers  a  striped  appearance.  Nuclei  are 
seen  here  and  there,  showing  that  the 
muscle  is  made  up  of  cells.  Such  is 
the  structure  of  muscle  fibers  which  are 
under  the  control  of  the  will,  the  vol- 
untary muscles  as  they  are  called.  If  it 
were  possible  to  prepare  muscle  fibers  in  such  a  manner  as  to  trace  the  path 
of  the  nerves  in  these  fibers,  such  nerves  would  be  seen  to  end  in  little 


A  bit  of  voluntary  muscle  fiber,  showing 
the  cross  striations  as  seen  under  the 
microscope. 


Motor  nerve  endings  in  striated  muscle 
fibers  as  seen  vmder  the  microscope. 


364 


HUMAN   PHYSIOLOGY 


A  bundle  of  involuntary  muscle  fibers,  as 
seen  under  the  microscope. 


knobs  or  plates  on  the  muscle  cells; 
thus,  the  action  of  every  muscle  fiber, 
perhaps  every  cell,  is  under  the  control 
of  the  nervous  system. 

Structure  of  Involuntary  Mus- 
cle.—  Muscles  in  which  the  movement 
is  not  controlled  by  the  will  are  called 
involuntary.  The  most  apparent  dif- 
ference between  voluntary  and  invol- 
untary muscle  fibers  (such  as  those 
found  in  the  wall  of  the  stomach  and 
intestines  of  man)  is  that  the  latter  do 
not  show  the  cross  striation  character- 
istic of  the  former.  The  involuntary 
fibers  are  supplied  with  blood  vessels 
and  nerves.  The  latter,  however, 
come  from  what  is  known  as  the  sym- 
pathetic  nervous  system.  Of  this  we 
shall  learn  more  later.  Fibers  from 
the  sympathetic  system  go  to  most 
organs  in  the  body 
cavity  of  man  —  the 
heart,  the  food  tube 
and  different  glands 
connected  with  it ; 
and  to  the  muscles  of 


the  blood  vessels.  The  act  of  breathing  and  the  heart-beat 
are  examples  of  an  automatic  muscular  action  where  ner- 
vous control  comes  largely  from  the  sympathetic  system. 
The  churning  movements  of  the  stomach  and  intestines 
are  examples  of  muscular  action  entirely  beyond  control 
of  the  will. 

Structure  of  Heart  Muscle.  —  Heart  muscle  differs 
slightly  in  appearance  from  both  voluntary  and  involun- 
tary muscle  fibers.  The  cross  striation  is  seen  here  as  in 
voluntary  muscle.  The  outline  of  the  individual  cells  can 
be  made  out  in  heart  muscle.     (See  diagram.) 

Rate  of  Muscular  Contraction.  —  A  wave  of  muscu- 
lar contraction  moves  rather  slowly  in  an  involuntary 
muscle;  a  little  more  rapidly  in  heart  muscle;  and  most 
rapidly  of  all  in  voluntary  muscle  fibers. 

Muscle  Tissue  and  its  Uses.  —  As  we  have  seen 
in  the  frog,  muscles  evidently  form  a  large  part  of 


?lii 


Striated  muscular 
fibers,  from  the 
heart  of  man,  di- 
vided by  trans- 
verse septa  into 
separate  nucle- 
ated portions, 
much  magaified 


MUSCLES 


365 


the  body.  In  man,  nearly  half  the  body  weight  is  muscle. 
Nearly  every  muscle  in  the  human  body  is  attached  to  a  bone 
either  at  one  or  at  both  ends.  Movement  is  performed  by  means 
of  the  muscles,  leverage  being  obtained  by  means  of  their  attach- 
ment to  the  bones.  Movement  is,  indeed,  the  chief  function  of 
muscles.  In  the  human  body  there  are  over  five  hundred  mus- 
cles, var}'ing  from  the  size  of  a  pinhead  to  a  band 
almost  two  feet  in  length.  Every  movement  of  the 
body,  be  it  merely  a  change  of  expression  or  change 
in  the  pitch  of  the  voice,  directly  results  from  con- 
traction or  expansion  of  a  muscle.  Muscles  also 
give  form  to  the  body,  and  are  useful  in  protecting 
the  delicate  organs  and  large  blood  vessels  within 
them. 


y] 


7 


Standing.  —  Certain  muscles  of  the  body  attached  to 
bones  are  used  in  standing.  These  are  muscles  of  the  legs, 
trunk,  and  neck.  Certain  joints  must  be  kept  rigid  by 
the  pull  of  flexor  and  extensor  muscles  attached  to  them; 
cooperation  of  muscles  with  the  central  nervous  system, 
especially  the  balancing  organ  in  the  ear,  must  also  be  had. 

Walking  and  Running.  —  Walking  is  more  difficult 
than  standing.  Two  sets  of  muscles  are  always  used,  one 
set  being  extended  while  the  other  set  is  contracted. 
Walking  may  be  considered  as  a  series  of  falls  in  a  forward 
direction,  equilibrium  being  maintained  by  putting  for- 
ward one  foot;  the  swinging  motion  of  the  arms  and 
swaying  of  the  body  aids  in  keeping  this  equilibrium.  Run- 
ning differs  from  walking  in  the  fact  that,  when  walking, 
one  foot  is  always  on  the  ground,  while  in  running,  a  brief 
period  exists  when  both  feet  are  off  the  ground. 


7n 


Diagram  of  some 
of  the  muscles 
which  tend  to 
keep  the  body 
erect. 


Work  done  by  Muscles.  —  The  heart  is  an  excel- 
lent example  of  an  organ  which  does  muscular  work. 
The  constant  pulsation  of  the  heart  during  one  day 
releases  energy  sufficient  to  raise  one  pound  434,112 
feet  from  the  earth's  surface.  During  this  period  the  heart  is 
estimated  to  rest  about  one  third  of  the  time  between  the  pulsa- 
tions. Thus,  it  is  evident  that  muscles  may  liberate  a  vast 
amount  of  energy;  in  order  to  do  this,  food  material,  which  is 
brought  by  the  blood  to  the  muscles,  must  be  oxidized.     As  we 


366  HUMAN   PHYSIOLOGY 

have  seen  in  the  frog,  muscles  are  well  supplied  with  blood  vessels: 
under  the  compound  microscope,  these  blood  vessels  are  observed 
to  break  up  into  tiny  capillaries  so  that  the  fibers  are  literally 
bathed  in  blood  and  lymph.  The  protoplasm  of  the  muscles 
takes  up  oxygen  from  the  blood;  this  oxygen  unites  with  the 
material  of  which  the  muscle  is  formed  or  with  food  which  is  brought 
there  by  the  blood;  as  a  result  of  the  oxidation,  carbon  dioxide 
is  given  up  and  carried  off  by  the  lymph;  nitrogenous  wastes 
(such  as  urea)  are  also  removed  in  the  lymph. 

How  Bodily  Heat  is  Produced.  —  When  coal  is  burned,  heat  is 
given  off;  this  heat  is  a  form  of  energy.  Food  and  tissues,  when 
oxidized,  also  give  off  heat.  When  muscles  are  exercised,  oxida- 
tion takes  place  more  rapidly,  and  more  heat  is  thus  produced. 
From  one  sixth  to  one  third  of  the  energy  produced  by  oxidation 
of  muscles  results  in  work;  two  thirds  to  five  sixths  of  it  is  given 
off  in  the  form  of  heat.  It  is  evident  that  the  high  body  tempera- 
ture is  thus  directly  due  to  the  oxidation  of  foods  or  tissues.  The 
heat  thus  produced  in  muscles  is  largely  dissipated  to  other  parts 
of  the  body  by  means  of  the  blood. 

When  an  extra  amount  of  heat  is  released  in  the  body,  the  blood 
is  allowed  to  go  to  the  skin,  and  heat  is  there  set  free :  An  increased 
amount  of  blood  sent  to  the  skin  favors  perspiration  by  increasing 
the  rate  of  evaporation;  this  leads  to  an  increased  loss  of  heat 
from  the  body. 

Necessity  of  Food  and  Fresh  Air  for  Muscles.  —  From  the  facts 
given  above,  it  is  evident  that  muscles  need  food  and  a  supply  of 
oxygen  in  order  to  perform  their  work.  Muscle,  although  a  large 
per  cent  is  made  up  of  water,  contains  proteid  as  its  principal 
solid  ingredient.  (This  may  be  proved  by  testing  a  bit  of  frog 
muscle  with  nitric  acid  and  ammonia.)  In  order  to  build  up  new 
muscle  to  replace  the  cells  which  are  worn  out  or  used  up,  proteid 
food  is  a  necessity.  Sugars,  which  are  energy-releasing  foods, 
can  be  utilized  in  moderate  amounts. 

Fresh  air  is  a  necessity  because  all  muscular  energy  is  released  as 
a  result  of  oxidation.  In  order  to  perform  muscular  work,  fresh 
air  containing  a  large  per  cent  of  oxygen  is  necessary.  It  is  essen- 
tial to  the  health  of  every  one,  even  a  sedentary  person,  that   a 


MUSCLES  36? 

good  supply  of  oxygen  be  provided,  especially  during  the  rest 
periods  at  night;  this  is  the  time  that  much  of  the  carbon  dioxide 
formed  in  the  tissues  during  the  day,  when  hard  work  is  done,  is 
eliminated. 

Rest  and  Exercise.  —  It  has  been  discovered  that  the  feeling  of 
muscular  fatigue,  the  feeling  of  utter  weariness  which  one  often 
has  after  prolonged  muscular  exertion,  is  probably  due  to  the  pres- 
ence of  waste  matters  in  the  muscle  and  blood.  These  wastes  are 
chiefly  the  products  of  oxidation, —  carbon  dioxide  and  urea. 

Exercise  in  moderation  is  directly  a  benefit  to  the  muscle. 
Each  time  a  muscle  does  work,  part  of  it  is  oxidized.  The  very^ 
process  of  oxidation  gives  the  muscle  an  opportunity  to  assimilate 
new  proteid  food;  this  results  directly  in  the  building  of  new 
muscle  cells  or  the  repairing  of  the  w^asted  ones. 

The  amount  and  kind  of  exercise  taken  depends  largely  on  the 
situation  of  the  individual.  A  strong  girl  or  boy,  brought  up  in  the 
country  with  fresh  air  in  abundance,  and  an  opportunity  to  do 
manual  labor  out  of  doors,  has  great  advantage  over  a  city  child. 
Exercise  in  a  gymnasium  is  not  nearly  of  so  much  benefit  as  out- 
of-door  work  and  play;  this  is  because  the  supply  of  oxj^gen,  even 
in  the  best-ventilated  room,  may  soon  be  at  least  partially  used  up 
and  carbon  dioxide  take  its  place  in  the  air.  The  best  results  are 
obtained  by  working  the  greatest  number  of  muscles  during  a 
given  period  of  time. 

When  we  become  moderately  warm,  after  exercise,  a  tepid  bath 
followed  by  a  cold  plunge  and  a  rub  down  brings  the  blood  to  the 
surface  of  the  body;  a  feeling  of  warmth  then  results  after  the  sud- 
den cooling  of  the  skin  by  the  cold  water. 

The  Relation  of  Alcohol  to  Muscular  Work.  —  Records,  compiled 
from  a  number  of  reliable  sources,  seem  to  show  that  alcohol  has 
a  very  decided  effect  upon  the  ability  of  a  man  to  perform  muscular 
work.  Not  only  does  it  affect  the  man  as  to  the  amount  of  work, 
but  as  to  the  quality  of  the  work  that  can  be  performed  in  a  given 
period  of  time.  The  following  extracts  show  plainly  the  relation 
of  alcohol,  even  in  moderate  quantities,  to  the  capacity  for  muscular 
work  and  to  the  performance  of  work  that  requires  great  accuracy 
and  training  of  the  eye  and  muscles. 


368  HUMAN   PHYSIOLOGY 

Experiments  have  been  made,  both  in  the  British  and  American 
armies,  testing  the  ability  of  soldiers  to  make  long,  forced  marches, 
some  regiments  having  been  supplied  with  a  liquor  ration  and 
others  without  it. 

''  There  are  experiments  which  show  that  men  may  do  an  in- 
creased amount  of  work  for  a  very  short  time  under  the  influence 
of  alcohol;  but  such  increase  is  accomplished,  as  the  above  ex- 
periments show,  only  at  the  expense  of  energy  or  tissue  which  is 
needed  for  bearing  sustained  labor  or  exposure.  Thus,  in  some 
experiments  upon  British  regiments,  the  regiment  which  had  liquor 
took  the  lead  at  the  start,  but  was  far  behind  at  the  finish."  — 
Hewes,  High  School  Physiology. 

"  The  sirdar.  Sir  Herbert  Kitchener,  and  General  Gatacre,  in 
their  advances  up  the  Nile,  have  strictly  forbidden  the  supply 
of  alcoholic  liquors  to  any  of  the  troops  under  their  command. 
We  learn  that  they  took  this  step  on  two  grounds.  First,  on  the 
ground  that  from  long  experience  they  were  convinced  that  the 
physical  condition  of  the  troops  would,  under  these  conditions, 
be  enormously  improved,  and  the  men  would  have  much  greater 
staying  power,  while  their  dash,  determination,  and  steadiness 
would  also  be  increased.  The  second  ground  appears  to  have 
been  that  the  mental  and  moral  stamina  of  the  troops  would  be 
preserved  in  a  far  greater  degree  than  could  possibly  be  the  case 
if  alcohol  were  served  out.  The  result  has  been  that  the  health, 
spirits,  and  conduct  of  the  troops  have  been  the  admiration  of 
all  those  who  have  had  any  dealings  with  them,  and  this  ex- 
periment on  a  large  scale  has  been  an  unqualified  success. '^  — 
J.  Sims  Woodhead,  M.D.,  Professor  of  Pathology  in  the  Uni- 
versity of  Cambridge,  England. 

"  The  attention  of  the  civilized  world  has  been  called  to  the 
conspicuous  fact  of  the  accuracy  of  the  firing  of  the  gunners  on 
our  battle  ships  in  the  recent  war  with  Spain.  The  contrast 
between  the  firing  of  the  men  of  our  navy  and  that  of  Spain  was 
due  in  part,  no  doubt,  to  the  custom  that  prevails  on  the  ships 
of  the  latter,  where  daily  rations  of  grog  are  given  at  all  times,  and 
when  an  action  is  going  on  or  anticipated,  double  rations  of  grog 
are  furnished  to  the  men;  while  since  1862,  when  that  custom  was 


MUSCLES  369 

abolished  by  our  government,  no  rations  of  liquor  are  allowed  at 
any  time  on  board  our  ships."  —  Hewes,  High  School  Physiology. 

"  The  custom  just  alluded  to  as  followed  by  Spain  is  true  of  all 
the  navies  of  the  world  but  ours.  Yet  Great  Britain  has  aban- 
doned the  double  rations  of  grog  when  a  fight  is  on,  and  then  no 
liquor  is  allowed;  but  in  place  of  it  supplies  of  water  and  oatmeal 
are  arranged  all  over  the  ship  to  satisfy  the  thirst  resulting  from 
the  heat,  exertion,  and  smoke  inseparable  from  a  naval  combat." 
—  The  Journal  of  the  American  Medical  Association,  January, 
1899,  p.  174. 

It  is  a  well-known  fact  that  all  athletes  who  go  into  training  for 
any  events  give  up,  for  the  time  at  least,  all  alcoholic  drinks  and 
tobacco. 

It  is  said  that  a  desire  to  excel  in  athletic  sport  has  led  clubs  of 
students  at  some  of  the  German  universities  to  give  up  their 
"  morning  drinking  bout."  They  have  learned  that  beer  drinking 
stands  in  the  way  of  their  best  physical  development  and  the 
highest  degree  of  athletic  success.  "  For  years  sports  have  been 
in  great  favor.  Some  of  these,  such  as  contests  between  boatmen 
or  between  cyclists,  require  considerable  energy  and  power  of 
endurance.  Evidently,  if  alcohol  increased  strength,  these  com- 
petitors would  provide  themselves  with  it  and  use  it  freely.  But 
this  is  not  the  case.  No  true  sportsman,  either  before  or  during 
the  contest,  touches  a  glass  of  spirits,  experience  having  taught 
the  harm  he  would  thereby  do  himself."  —  De  Bienfait,  of  Liege. 

Effect  of  Alcohol  and  Other  Stimulants  and  Narcotics  upon 
Muscular  Action.  —  ''  The  most  serious  effects  of  the  excessive 
use  of  alcohoUc  drinks,  tobacco,  opium,  chloral,  and  other  narcotic 
drugs  are  felt  by  the  nervous  system  and  will  be  most  fully  treated 
when  we  come  to  the  special  study  of  that  part  of  the  human 
organism.  But  it  is  well  to  notice  here  how  those  substances 
influence  the  organs  of  motion. 

*'  No  one  who  has  ever  seen  a  drunken  man  in  the  stage  pre- 
ceding that  of  stupor  can  have  failed  to  observe  the  uncertainty 
of  his  muscular  movements:  the  shaking  hand,  the  staggering 
gait,  the  thick,  indistinct  utterance.  These  effects  are  due  to 
what  is  called  the  excessive  use  of  alcohohc  drinks,  and  no  one 

hunter's  BIOL.  —  24 


370  HUMAN   PHYSIOLOGY 

doubts  that  in  large  quantities  they  act  injuriously  upon  the  sys- 
tem. Alcohol  deranges  the  action  of  the  muscles  by  its  influence 
upon  the  nervous  system,  causing  defective  regulation  of  the 
supply  of  nervous  force  to  the  several  muscles.  As  to  whether 
it  is  possible  to  use  alcohol  in  small  amounts  without  impairing 
the  perfection  and  vigor  of  muscular  action,  there  is  one  very 
significant  fact :  that  men  in  training  for  severe  muscular  exertion 
in  athletic  contests  are  strictly  forbidden  the  use  of  alcohol 
in  any  form  and  in  any  quantity,  whether  or  not  they  have  been 
previously  accustomed  to  such  indulgence.  As  the  rules  for  such 
training  are  the  result  of  long  and  wide  experience  and  most  care- 
ful study,  it  is  safe  to  conclude  that  alcohol  at  least  does  not  pro- 
mote strength,  endurance,  or  precision  of  muscular  movement. '^ 
—  Macy,  Physiology. 

Effect  of  Tobacco  on  Muscles.  —  The  stunting  effect  of  tobacco 
on  the  growth  and  development  of  the  muscles  is  well  known. 
Every  teacher  of  gymnastics  knows  this;  hence  tobacco  is  not 
allowed  to  the  athlete.  Another  reason  why  the  man  in  training 
is  not  allowed  tobacco,  is  because  of  its  paralyzing  effect  upon  the 
nerve  cells  controlling  the  movement  of  muscles,  this  diminishing 
or  inhibiting  the  nervous  energy  which  a  man  uses  in  the  exercise 
of  his  muscles. 

'^  Tobacco  and  other  narcotics  also  affect  muscular  activity 
through  their  effect  upon  the  nerves.  All  narcotics  have  as  their 
natural,  characteristic  influence  the  paralyzing  of  some  of  the 
nerve  centers.  As  medicines  they  may  give  relief  from  pain  and 
so  act  beneficently  under  skillful  application.  Tobacco  has  a 
special  effect  upon  the  nerve  centers  regulating  the  action  of  the 
muscles  of  the  heart,  making  that  action  irregular  and  less  vigor- 
ous. This  is  particularly  true  of  the  young,  and  it  is  not  very 
uncommon  for  boys  addicted  to  excessive  cigarette  smoking  to 
develop  serious  disease  of  the  heart,  or  even  to  die  suddenly  from 
'heart   failure.'''  —  MacY;  Physiology, 


XXXII.     THE  SKELETON 


General  Structure  and  Uses  of  the  Skeleton.  —  First,  bones  form 
a  framework  to  which  muscles  are  attached;  thus  they  are  used 
as  levers  for  purposes  of  movement.  Second,  they  give  protection 
to  delicate  organs ; 
they  form  a  case 
around  the  brain,  and 
spinal  cord;  as  ribs 
they  protect  the  or- 
gans in  the  body  cav- 
ity. Third,  they  give 
rigidity  and  form  to 
the  body. 

Laboratory  Work  on 
the  Skeleton  of  a  Frog; 
Comparison  with  the  Skel- 
eton of  Man.  —  For  this 
purpose,  clean  skeletons 
of  the  frog  (these  may 
be  prepared  by  careful 
students)  and  a  prepared 
skeleton  of  man  may  be 
used.  This  exercise  may 
be  made  of  increased 
value  by  using  skeletons 
of  several  different  ver- 
tebrates, for  example,  a 
bony  fish,  frog,  snake, 
bird,  dog  or  cat,  and 
rnan.  The  different  re- 
gions may  be  identified  and  homologies  and  analogies  drawn  between  dif- 
ferent bones  and  organs  in  the  various  skeletons. 

The  skeleton  of  vertebrate  animals  consists  of  two  distinct  regions :  a 
vertebral  column  or  backbone  which,  with  the  skull,  forms  the  axial  skeleton; 
and  the  parts  attached  to  this  main  axis,  the  appendicular  skeleton  (the 
appendages).  All  skeletons  of  vertebrates  have  the  same  general  regions, 
the  size  and  shape  of  the  bones  in  these  regions  differing  somewhat  in  each 
kind  of  animal. 

In  the  axial  skeleton  of  the  frog,  as  well  as  in  man,  the  vertebral  column 
is  made  up  of  a  number  of  bones  of  irregular  shape,  which  fit  more  or  less 
closely  into  each  other.     These  bones  are  called  vertebrw.      Notice  that  the 

371 


Skeleton  of  the  frog;  S.,  skull;  SC,  scapula;  R.U.,  radio 
ulna;  H.,  humerus;  Ph.,  phalanges;  MC,  metacarpals; 
C,  carpals;  V.,  vertebral  column;  UR.,  urostyle;  P.G., 
pelvic  girdle;  F.,  femur;  TF.,  tibia  and  fibula;  TS., 
tarsals;  MT.,  metatarsals. 


372 


HUMAN   PHYSIOLOGY 


vertebrae  possess  long  processes  to  which 
muscles  of  the  back  are  attached. 
Compare  the  vertebral  column  of  the 
frog  and  man  in  the  following  respects : 
Is  there  a  distinct  neck  region?  Are 
ribs  present  ?  Are  the  ribs  attached  to 
the  vertebrae?  How  many  vertebrae 
in  man  bear  ribs  ?  In  man  a  flat  bone 
to  which  certain  of  the  ribs  are  at- 
tached is  found  on  the  ventral  midline 
of  the  skeleton.  This  bone,  called  the 
sternum,  is  so  small  in  the  frog  that  you 
will  not  be  able  to  see  it.  Are  all  the 
ribs  in  man  attached  to  the  breastbone 
or  sternum  ?  How  many  ribs  are  free 
from  the  breastbone?  Notice,  in  the 
frog,  the  peculiar  long  bone  at  the  pos- 
terior end  of  the  spinal  column;  this 
bone  is  called  the  urostyle.  No  homol- 
ogous bone  is  found  in  man.  Look  at 
the  vertebral  column  of  man;  notice 
that  it  is  shaped  somewhat  like  the 
letter  S.  The  bodies  of  the  vertebrae, 
piled  one  upon  the  other,  form  a  col- 
umn of  enough  strength  to  support  the 
whole  body.  The  double  curve  of  the 
vertebral  column  combines  elasticity 
with  strength. 

Structure  of  a  Vertebra  in  Man. — 
Observe  a  single  vertebra  of  man;  it 
will  be  found,  in  a  general  way,  to  con- 
sist of  two  regions,  a  solid  rounded  por- 
tion called  the  centrum  or  body,  and  a 
bony  arch  from  which  are  given  off  the 
processes  referred  to  above.  Within 
this  arch  (called  the  neural  arch)  is 
found  the  spinal  column  or  nerve  cord. 
Thus,  the  vertebrae  form  a  wonderful 
protection  for  this  most  delicate  of  all 
organs;  and,  with  the  bony  covering 
of  the  skull,  protect  the  central  nervous 
system. 


Skeleton  of  man;  CR.,  cranium;  CL., 
clavicle;  ST.,  sternum;  SC,  scapula; 
H.,  humerus;  V.C.,  vertebral  column; 
R.,  radius  and  ulna;  P.,  pelvic  girdle; 
C,  carpals;  MC,  metacarpals;  Ph., 
phalanges;  F.,  femur;  Fi.,  fibula;  T. 
tibia;  Tar.,  tarsals;  MT.,  metatarsals. 


Adaptations  in  the  Vertebral 
Column. — The  vertebral  column 
in  man  is  made  up  of  many  sepa- 
rate pieces  of  bone:  thirty-three 
in  a  child;  twenty-six  in  the  adult, 
several  bones  in  the  region  of  the  pelvis  later  growing  together. 
Each  vertebra  presents  the  general  form  of  a  body  or  centrum  of 
bone  and  a  bony  arch  with  seven  projections;  in  this  arch  runs 


THE  SKELETON 


373 


the  spinal  cord.  The  surface  of  the  centrum  and  those  parts  of 
the  vertebrae  each  of  which  fits  into  its  next  neighbor  are  covered 
with  pads  of  cartilage.  Two  of  the  processes  in  each  vertebra 
project  forward  and  two  backward;  these  form  articulations  or 
joints  with  the  neighboring  vertebrsB.  Of  the  other  processes, 
one  projects  dorsally  and  two  project  laterally;  these  give  attach- 
ment to  the  muscles  of  the  back.  The  two  vertebrae  directly  be- 
neath the  head  are  modified  so  as  to  permit  the  skull  to  rest  in  the 
upper  one;  this  articulates  freely  with  the  second  vertebra,  thus 
permitting  of  the  nodding  and  turning  movements  of  the  head. 
Besides  these  individual  adaptations,  the  vertebral  column,  as  a 
whole,  is  peculiarly  adapted  to  pro- 
tect the  brain  from  jar;  this  is  seen 
in  the  double  bend  of  the  vertebral 
column  and  the  pads  of  cartilage  be- 
tween the  individual  vertebrae.  The 
whole  column  of  vertebrae  joined 
each  to  the  other  supports  the  weight 
of  the  body.  The  largest  vertebrae 
at  the  base  are  joined  to  the  huge 
pelvic  bones  for  the  better  support 
of  the  body  above.  That  part  of  the 
vertebral  column  of  man  which  bears  the  ribs  is  known  as  the 
thoracic  region.  The  ribs,  twelve  in  number,  are  long  bones 
which  combine  lightness  with  strength;  joined  by  elastic  cartilage 
to  the  sternum  in  front  and  to  the  vertebrae  behind,  they  form  a 
wonderful  protection  to  the  organs  in  the  thoracic  cavity  and  j^et 
allow  free  movement  in  breathing.  That  part  of  the  skeleton 
to  which  the  bones  of  the  anterior  and  posterior  appendages  are 
attached  are  respectively  known  as  the  pectoral  girdle  (from 
which  hangs  the  arm)  and  the  jpelvic  girdle  (which  joins  the  leg 
bones  to  the  axial  skeleton). 

The  Appendages.  —  The  bones  of  the  appendages  attached  to 
the  pectoral  and  pelvic  girdles  are  adapted  peculiarly  to  locomo- 
tion and  support;  for  this  purpose  the  bones  are  long  and  strong, 
hinged  by  very  flexible  joints.  The  latter  are  especially  free  in 
the  hand  to  allow  for  grasping.     In  the  leg,  where  weight  must  be 


Vertebra,  showing  attachment  of 
ribs;  C,  centrum;  i2.,  ribs ;  SP., 
spinous  process. 


374  HUMAN   PHYSIOLOGY 

supported  as  well  as  carried,  the  bones  are  bound  more  firmly  to 
the  axial  skeleton.  The  bones  of  the  foot  are  so  arranged  that  a 
springy  arch  is  formed  which  aids  greatly  in  locomotion. 

Pelvic  Girdle  and  Leg.  Laboratory  Exercise. — The  lower  end  of  the 
vertebral  column  in  man,  as  in  the  frog,  is  united  with  a  number  of  broad 
bones  which  together  form  the  pelvic  girdle.  Notice  the  difference  in  the 
shape  and  position  of  the  pelvic  girdle  in  the  frog  and  in  man.  In  man, 
the  pelvic  bones  support  the  organs  of  the  body  cavity;  this  is  a  peculiar 
adaptation  to  the  upright  position  of  man.  Compare  the  bones  of  the  hind 
leg  of  the  frog  with  those  of  the  human  skeleton.  Beginning  with  the  large 
bones  next  the  pelvic  girdle,  these  bones  are :  the  thigh  bone,  or  femur; 
the  shank  bones,  or  tibia  and  fibula  (the  tibia  and  fibula  are  united  into  one 
bone  in  the  frog;  the  tibia  is  the  larger  bone  in  man;  it  is  on  the  side  of 
the  big  toe);  the  ankle  bones,  or  tarsals;  foot  bones,  or  metatarsals;  and 
the  bones  of  the  toe,  phalanges,  so-called  from  the  arrangement  which  is 
somewhat  like  a  Greek  phalanx  of  soldiers.  Compare  the  relative  size, 
shape,  and  number  of  the  bones  of  the  foot  and  ankle  in  the  frog  and  in  man. 
Can  you  explain  the  differences  which  occur  as  an  adaptation  to  the  life 
which  the  animal  leads  ? 

Bones  of  the  Pectoral  Girdle  and  Arm.  — -Compare  the  attachment  of  the 
fore  limb  of  the  frog  with  that  of  man.  The  bones  which  attach  the  fore 
limb  to  the  axial  skeleton  collectively  form  the  pectoral  girdle.  Find  in 
the  frog  the  fiat  shoulder  blade  (not  quite  homologous  with  the  shoulder 
blade  or  scapula  of  man).  The  collar  bone  or  clavicle  is  not  plainly  seen 
in  the  frog;  note  its  position  in  the  human  skeleton.  (See  page  372.)  Now 
compare  the  bones  of  the  fore  limb  of  a  frog  and  in  man.  The  large  stout 
bone  of  the  upper  arm  is  the  humerus;  the  two  bones  of  the  forearm  (united 
in  the  frog)  are  the  ulna  and  radius;  the  latter  is  on  the  thumb  side  of  the 
arm.  The  bones  of  the  wrist  are  known  as  car  pals;  those  of  the  palm  of 
the  hand,  metacarpals ;  those  of  the  fingers,  the  phalanges. 

Notice  how  the  fore  limb  of  a  frog  is  shortened.  The  thumb  is  almost 
completely  lost.  Is  this  an  adaptation  to  the  frog's  mode  of  life  ?  Give 
reasons. 

Comparison  of  the  Skull  of  the  Frog  with  that  of  Man.  —  Notice  the  differ- 
ence in  the  general  shape  of  the  head  and  the  lack  of  a  neck  in  the  frog. 
In  man,  two  groups  of  bones  make  up  the  skull,  the  bones  of  the  face  and 
those  of  the  brain  case  or  cranium.  In  the  frog,  this  distinction  is  not  so 
easily  seen.  Notice  the  upper  and  lower  jawbones  in  man.  Do  they 
bear  teeth  ?  Do  you  find  corresponding  bones  that  bear  teeth  in  the  frog  ? 
Are  both  jaws  moved  in  talking  or  chewing?  Notice  how  much  larger, 
relatively,  the  cranium  in  man  is  than  that  of  the  frog.  Notice  in  man 
that  the  bones  of  the  cranium  are  dovetailed  together,  such  joints  being 
known  as  sutures. 

The  Human  Skull.  —  In  man,  the  cranium  is  a  box  made  up  of  eight 
bones.  This  is  adapted  to  protect  the  delicate  brain.  Of  the  eight  bones, 
four  are  paired :  the  two  parietals,  which  form  a  large  part  of  the  crown  of 
the  head,  and  the  temporals,  which  inclose  the  ear  cavities.  Of  the  four  sin- 
gle bones,  two  are  easily  found;  the  frontal,  forming  the  forehead  and  upper 
part  of  the  eye  sockets,  and  the  occipital,  covering  the  base  of  the  brain.  In 
the  occipital  bone  is  a  large  opening,  through  which,  in  life,  the  spinal  cord 


THE  SKELETON 


375 


passes.  Part  of  the  base  of  the  cranium  is  formed  by  the  sphenoid  and  eth- 
moid bones.  Part  of  the  former  bone  extends  upward  between  the  frontal 
and  temporal  bones.  The  skull  shows  wonderful  adaptations  for  its  varied 
functions.  The  brain  case  is  compactly  built,  its  arched  roof  giving 
strength.  The  eye  and  inner 
ear  are  protected  in  sockets 
of  bone.  The  lower  jaw  works 
upon  a  hinge,  and  furnishes 
attachment  for  strong  mus- 
cles which  move  the  jaw.  Try 
to  add  other  adaptations  to 
this  list. 


Long  bone;  C,  internal  cavity; 
H.B.,  hard  bone;  S.B.,  spongy  bone. 


The  skull;  F.,  frontal  bone;  P.,  parietal  bone;  T., 
temporal  bone  ;  SP.,  sphenoid  bone;  O.,  occipital 
bone ;  U.J.,  superior  maxillary  (upper  jaw)  bone  ; 
L.J.,  inferior  maxillary  (lower  jaw)  bone. 

Internal  Structure  of  a  Long  Bone. 
Laboratory  Exercise.  —  A  better  under- 
standing may  be  gained  of  the  internal 
structure  of  the  long  bone  from  observa- 
tions made,  for  example,  on  a  long  leg 
bone  of  a  sheep  (obtained  fresh  from  the 
butcher).  In  such  a  bone,  notice  the 
rounded  ends;  these  are  covered  during 
life  by  a  layer  of  gristle  (cartilage). 
Notice  also  the  roughened  projections 
(called  processes)  which  serve  for  the  at- 
tachment of  muscles.  What  parts  of  the 
bone  are  provided  with  such  projections  ? 
In  a  bone  cut  lengthwise,  notice  that  the 
outer  surface  is  covered  with  a  thin  layer 
of  connective  tissue;  this  is  called  the 
periosteum.  The  periosteum  permits  of 
the  entrance  into  the  bone  of  blood  vessels 
and  nerves.  It  also  forms  bone  from  its 
inner  surface.  In  cases  of  injurj^  the 
bone  inside  the  periosteum  ma}'  be  re- 
moved by  a  surgeon.  New  bony  tissue 
will  then  be  rebuilt  by  the  periosteum. 
Notice  also  the  difference  between  the  end 
of  the  bone  and  the  middle  part  or  shaft. 
The  entire  outer  layer  is  compact;  the 
inner,  spongy  in  structure.  Where  is  the 
most  compact  mass  of  the  bone?     The 


376  HUMAN   PHYSIOLOGY 

most  spongy  area  ?  Find  the  marrow  which  partially  fills  the  central  cavity. 
What  is  its  color  ?  Blood  vessels  and  nerves  pass  into  the  marrow  through 
small  openings  in  the  compact  bone.  Try  to  find  a  rather  large  opening 
(near  one  end)  through  which  the  artery  passes  into  the  bone.  Draw  in 
your  notebook  a  bone  cut  lengthwise,  and  label  all  the  parts  in  the  drawing. 

A  long  bone  of  the  human  body  shows  the  same  general  charac- 
teristics as  above  described.  The  surface  of  the  bone  is  covered 
with  periosteum  or  connective  tissue.  Under  the  periosteum  is 
found  a  layer  of  hard,  compact  bone.  This  covers  a  layer  of  spongy 
bony  tissue  under  the  heads  or  ends  of  the  bone.  The  ends  of  the 
bone  are  covered  with  pads  of  cartilage.  The  internal  cavity  is 
filled  with  yellow  marrow,  the  cells  of  which  contain  considerable 
fat. 

Home  Experiment.  — •  Rub  some  marrow  on  a  piece  of  paper.  Hold 
the  paper  to  the  light.     What  substance  is  present? 

Structure  of  a  Flat  Bone.  Laboratory  Exercise.  —  Compare  the  long  bone 
with  aflat  one,  for  example,  a  rib.  The  following  differences  in  structure 
will  be  noted.  The  outer  wall  is  hard  bone  as  in  the  leg  bone.  The  entire 
interior,  however,  is  made  up  of  spongy  tissue,  its  spaces  being  more  or  less 
completely  filled  with  red  marrow.  We  thus  find  that  in  all  long  bones, 
where  strength  must  he  combined  with  lightness,  the  bone  is  hollow.  For 
example,  in  birds,  most  of  the  large  bones  contain  air  spaces ;  the  weight  of 
the  bird  is  thus  decreased,  a  peculiar  adaptation  for  flight.  In  a  flat  bone, 
lightness  and  strength  are  obtained  by  having  a  layer  of  solid  bone  outside 
the  soft  spongy  material. 

Substances  present  in  Bone.  Home  Experiment.  —  Burn  a  bone  in  a  hot 
fire.  This  removes  the  animal  material.  Now  test  with  hydrochloric 
acid.  What  happens?  Leave  another  bone  for  several  days  in  10  to  20 
per  cent  hydrochloric  acid  solution.  The  mineral  matter  is  thus  removed. 
After  the  bone  has  been  taken  from  the  acid,  it  may  be  bent  or  twisted 
into  knots  without  breaking. 

The  bone-making  cells  make  bony  tissue  largely  from  lime. 
This  is  easily  shown  by  the  above  experiments.  Some  other 
mineral  matters  are  left  behind  after  testing  for  lime,  common 
table  salt  and  silica  being  the  most  abundant.  These  materials 
are,  of  course,  taken  into  the  body  with  food. 

Growth  of  the  Skeleton.  —  In  some  of  the  lower  animals  studied, 
for  example  the  limy  sponge,  we  found  certain  cells  of  the  animal 
take  up  lime  from  the  water  or  food  taken  into  the  body  and  lay 
this  down  as  a  secretion  in  the  form  of  spicules.  In  somewhat 
the  same  manner  certain  cells  undertake  the  work  of  skeleton 
formation  in  man.  Water,  milk,  and  other  foods  furnish  the 
mineral  matter  necessary.     The  result  is  that  the  skeleton  grows 


THE  SKELETON 


377 


continually,  both  from  the  inside  and  the  outside  surface  of  bone. 
Early  in  life,  when  the  skeleton  grows  rapidly,  the  living  part  of 
bone  exceeds  the  mineral  matter  in  it.  Bones  of  young  people  are 
frequently  quite  soft  and  flexible.  Very  early  in  life,  almost  all 
bones  are  formed  of  a  tissue  called  cartilage. 

Microscopic  Structure  of  Bone.  — Gristle,  the  common  name  for  car- 
tilage, is  seen  under  the  microscope  to  be  made  up  of  living  cells  surrounded 
by  a  clear,  tough  material, 
the  latter  formed  by  the 
action  of  the  cells  embedded 
in  it.  Formation  of  bone 
takes  place  in  much  the 
same  way.  In  a  piece  of 
bone  examined  under  the 
microscope  are  found  hun- 
dreds of  little  irregular 
spaces.  From  these  spaces 
radiate  many  tiny  canals. 
These  spaces,  during  the 
life  of  the  animal,  were 
occupied  by  bone-forming 
cells,  irregular  processes 
from  which  passed  out  into 
the  canals.  Later,  limy  mat- 
ter was  deposited  around  certain  of  the  cells.      Thus  true  bone  was  formed. 

Hygiene  of  the  Skeleton;  Differences  in  Structure  of  the  Skele- 
ton OF  A  Child  and  an  Adult.  —  During  childhood,  because  of  the  small 
amount  of  mineral  matter  and  consequent  lack  of  rigidity  in  bone,  we  must 
exercise  some  care  in  the  treatment  of  the  skeleton.  A  round-shouldered 
condition,  brought  on  by  sitting  in  an  incorrect  position,  may  cause  a  promi- 
nent deformity  of  the  skeleton.  Children  are  frequently  allowed  to  walk 
before  the  leg  bones  are  capable  of  supporting  the  weight  of  the  body,  thus 
causing  bow-leggedness.  Seats  at  school  which  force  a  child  to  take  an  incor- 
rect attitude  when  at  rest  are  frequently  the  means  of  permanently  deforming 
the  vertebral  column.  Later  in  life,  when  the  activity  of  the  bone-forming 
cells  ceases,  more  mineral  matter  is  present  than  animal  matter.  A  broken 
bone  is  thus  much  more  serious  at  this  time  than  in  a  young  person. 


Bone,  as  seen  under  the  microscope. 


Joints 

Movement  in  the  Hind  Leg  of  the  Frog.  —  In  the  hind  leg  of  the  frog  pre- 
viously studied,  cut  through  the  muscles  of  the  thigh  to  the  bone;  make 
out  exactly  how  and  where  the  muscles  of  the  thigh  are  attached  to  the 


378 


HUMAN   PHYSIOLOGY 


bone ;  move  the  leg  in  as  many  different  directions  as  possible ;  notice  that 
it  may  be  flexed  or  bent ;  that  it  may  be  extended  to  its  original  position ; 
that  it  may  be  rotated;  that  it  may  be  moved  to  and  from  the  midline 
of  the  body;  that,  with  the  knee  held  stiff,  the  whole  limb  may  be  made  to 
describe  the  arc  of  a  circle. 

These  same  movements  are  possible  in  the  leg  of  a  man.  This  move- 
ment between  bones  is  obtained  by  means  of  joints.  If,  in  the  frog,  we  care- 
fully separate  the  muscles  of  the  thigh  to  the  bone,  we 
find  that  they  are  attached  to  the  bone  by  white,  glis- 
tening tendons.  Careful  examination  shows  that  the 
bones  themselves  are  held  together  by  very  tough  white 
bands  or  cords;  these  are  the  ligaments.  We  find,  too, 
that  one  end  of  the  large  thigh  bone  fits  into  a  socket 
in  the  hip  bone  or  pelvic  arch.  It  is  thus  easy  to  see 
how  such  free  movement  is  obtained  in  the  leg. 

Ball  and  Socket  Joint.  —  Such  a  joint  as  just 
described  is  called  a  hall  and  socket  joint.     In 

Ball  and  socket  joint.  ,i  irxT_i         •        ii.*j" 

man  the  movement  oi  the  leg  is  obtained  in  ex- 
actly the  way  described  for  the  hind  leg  of  the  frog.  The  two 
best  examples  of  a  ball  and  socket  joint  are  found  between  the 
long  bone  in  the  arm  and  the  shoulder,  and  between  the  bones  of 
the  hip  and  the  long  bone  of  the  leg. 

Hinge  Joints.  —  The  second  kind  of  joint,  in  the  leg  of  the  frog,  is  found 
between  the  thigh  and  the  shank.  Notice  that  movement  here  occurs 
freely  in  only  two  directions,  backward  and  forward ;  hence 
this  is  called  a  hinge  joint.  In  man  the  best  examples  of 
a  hinge  joint  are  found  in  the  knee  and  elbow;  others  are 
in  the  fingers  and  toes. 

Gliding  Joints.  —  Another  form  of  joint,  best  seen  in 
the  skeleton  of  man,  is  a  sliding  or  gliding  joint.  Here 
the  range  of  movement  is  slight.  Gliding  joints  are  found 
between  the  vertebrse  or  bones  of  the  vertebral  column 
(backbone). 

Pivot  Joints.  —  Another  rather  unusual  joint  is  the 
pivot  joint.  This  is  best  seen  between  the  skull  of  man 
and  the  topmost  bone  of  the  vertebral  column.  The  skull 
is  held  in  place  by  means  of  two  small  knobs  which  pro- 
ject downward  and  rest  in  cavities  in  the  bone  directly 
beneath  them. 

Levers  in  the  Body.  —  It  is  evident  that  movement 
of  a  joint  is  caused  by  muscles  which  act  in  cooperation 
with  the  bones  to  which  they  are  attached  ;    the  latter 
form  true  levers.     A  lever  is  a  structure  by  which  either  greater  work  power 
or  greater  range  of  motion  is  obtained.      In  this  apparatus,  the  lever  works 


Hinge  joint,  show- 
ing muscle  (a) 
and  its  tendon 
(6). 


THE  SKELETON  379 

against  a  fixed  point,  the  fulcrum,  in  order  to  raise  a  certain  weight.  A 
seesaw  is  a  lever;  here  the  fulcrum  is  in  the  middle,  the  weight  is  at  one 
end,  and  the  power  to  lift  the  weight  is  applied  at  the  other  end.  There 
are  three  classes  of  levers,  named  according  to  the  position  of  the  fulcrum. 

In  the  first  class,  the  fulcrum  lies  between  the  weight  and  the  power; 
the  seesaw  is  an  example  of  this.  The  best  example  in  the  human  body,  of 
a  lever  of  the  first  class,  is  seen  when  the  head  nods.  Here  the  fulcrum  is  the 
vertebra  known  as  the  atlas;  the  power  is  the  muscles  of  the  neck  attached 
to  the  back  of  the  skull  and  to  the  spine ;  the  weight  is  the  front  part  of  the 
head.  When  one  keeps  the  head  erect,  this  lever  is  used;  the  nodding 
head  when  one  is  sleeping  shows  this  plainly. 

A  lever  of  the  second  class  has  the  fulcrum  at  one  end,  and  the  weight 
between  it  and  the  power;  when  we  rise  on  our  toes,  we  use  this  kind  of 
lever.     Try  to  explain  this  by  referring  to  a  skeleton  of  a  frog  or  of  man. 

In  a  lever  of  the  third  class,  the  fulcrum  is  at  one  end,  with  the  power 
between  it  and  the  weight.  This  is  the  kind  of  lever  seen  most  frequently 
in  the  human  body.  The  flexing  (drawing  up)  of  the  lower  leg  or  the  fore- 
arm is  an  example  of  the  use  of  this  kind  of  lever.  In  such  a  lever,  a  wide 
range  of  movement  is  obtained. 

Sprains.  —  A  sudden  strain  or  twisting  in  the  region  of  a  joint  may 
result  in  the  pulling  out  or  tearing  of  the  ligaments  or  tendons  of  that 
joint.  Such  an  injury  may  be  recognized  by  the  sudden  swelling  in  that 
region,  followed  by  great  pain.  A  cure  of  the  sprain  is  effected  only  by 
nature's  own  remedy,  complete  rest.  For  immediate  relief  hot  water 
applications,  followed  by  arnica  or  some  liniment,  are  best;  a  tight  bandage 
should  be  applied  at  once  and  a  doctor  called  as  soon  as  possible. 

Dislocations.  —  The  bones  of  a  joint  may  be  accidentally  forced  apart. 
Such  a  separation  is  called  a  dislocation  and  is  known  by  the  intense  pain 
which  follows  any  attempt  to  move  the  joint.  There  is  often  considerable 
swelling  of  the  affected  part;  the  bone  may  even  protrude.  A  physician 
should  be  called  at  once  so  that  the  bone  may  be  slipped  into  place  again. 
Hot  or  cold  water  applied  to  the  joint  and  rest  in  a  comfortable  position 
should  be  given  until  the  doctor  comes. 

Fractures.  —  A  break  or  fracture  usually  occurs  in  one  of  the  long  bones 
of  the  body.  The  clavicle  or  collar  bone  (easily  felt  in  the  front  part  of 
the  shoulder  below  the  neck),  because  of  its  exposed  position,  is  most 
frequently  broken.  The  immediate  treatment  for  fracture  is  rest  in  a 
comfortable  position;  cold  water  applications  may  relieve  the  pain.  Send 
for  a  doctor  at  once.  To  heal  a  fracture,  it  is  necessary  to  bring  the  two 
broken  ends  of  the  bone  together,  and  hold  them  so  that  they  will  grow 
together  or  knit;   for  this  purpose  splints  are  often  employed. 


XXXIII.     RESPIRATION 


Necessity  for  Respiration.  — We  have  seen  that  plants  and  animals 
need  oxygen  in  order  that  the  life  processes  may  go  on.  Food  is 
oxidized  to  release  energy,  just  as  coal  is  burned  to  give  heat  to 
run  an  engine.  As  a  draft  of  air  is  required  to  make  a  fire  under 
the  boiler,  so,  in  the  human  body,  oxj^gen  must  be  given  so  that 

foods  or  tissues  may  be  oxidized  to  re- 
lease energy  used  in  growth.  Blood,  in 
its  circulation  to  all  parts  of  the  body,  is 
the  medium  which  conveys  the  oxygen  to 
that  place  in  the  body  where  it  will  be 
used.  But  where  does  the  blood  get 
this  supply  of  oxygen?  We  have  al- 
luded, in  Circulation,  to  the  fact  that 
the  lungs  are  the  organs  which  give 
oxygen  to  the  blood  and  take  from  it 
carbon  dioxide.  Let  us  examine  the 
organs  used  by  the  frog  in  breathing, 
and  see  if  this  matter  becomes  any 
plainer. 


Lungs  of  a  frog ;  baglike  exten- 
sions of  the  windpipe. 


Study  of  the  Organs  of  Respiration  in  the  Frog;  Comparison  with  Man.  — 
Notice  the  pumping  movement  in  the  throat  as  a  frog  breathes.  The  frog 
swallows  air.  Does  this  method  differ  from  breathing  in  man?  How 
and  where  are  the  nostril  holes  (nares)  placed?  How  is  this  of  advantage 
to  the  animal?  Do  you  notice  any  movement  of  the  nares  in  breathing? 
Use  a  preserved  frog  for  the  following  exercise  •  Open  the  mouth  of  the  frog, 
and  find  the  openings  in  the  roof  of  the  mouth,  leading  from  the  anterior 
nares.  Find  a  vertical  slit  in  the  floor  of  the  throat.  This  is  the  glottis 
or  opening  to  the  windpipe.  If  the  muscles  be  carefully  removed  from  the 
ventral  surface  of  the  body  just  beneath  the  arms,  and  a  careful  incision 
made,  the  windpipe  may  be  seen.  Notice  that  it  branches  into  two  smaller 
tubes,  each  of  which  leads  to  a  lung.  These  tubes  are  the  bronchi.  The 
lungs  are  two  spongy  bags,  the  walls  of  which  are  filled  with  tiny  blood 
vessels.  Inflate  the  lungs  by  inserting  a  blowpipe  in  the  glottis  and  blow- 
ing into  it.     Are  the  lungs  elastic? 

The  Organs  of  Respiration  in  Man. — The  course  of  air  passing 
from  the  outside  of  the  lungs  in  man  is  much  the  same  as  in  the 

380 


RESPIRATION 


381 


frog.  Air  passes  through  the  nares,  the  glottis,  and  into  the 
windpipe.  This  cartilaginous  tube,  the  top  of  which  may  easily 
be  felt  as  the  Adam's  apple 
of  the  throat,  divides  into 
two  bronchi.  The  bronchi 
within  the  lungs  break  up 
into  a  great  number  of 
smaller  tubes,  the  bronchial 
tubes,  which  divide  some- 
what like  the  small  branches 
of  a  tree.  This  branching 
increases  the  surface  of  the 
air  tubes  within  the  lungs. 
The  bronchial  tubes,  indeed 
all  the  air  passages,  are 
lined  with  ciliated  cells. 
The  cilia  of  these  cells  are 
constantly  in  motion,  beat- 
ing with  a  quick  stroke  toward  the  outer  end  of  the  tube,  that  is, 

toward    the    mouth.      Hence 


/-f-j 


Air  passages  in  the  human  lungs;  a,  larynx;  h,  tra- 
chea (or  windpipe);  c,  c?,  bronchi;  e,  bronchial 
tubes;  /,  cluster  of  air  cells. 


-^^, 


Bronchiole 


Diagram  of  two  air  cells,  showing  the  capillary 
network  which  covers  them,  and  at  a  the 
structures  which  intervene  between  the  air 
and  the  blood  are  indicated;  /,  mucous 
membrane  of  the  air  cell;  2,  submucous 
mesh  work;  3,  wall  of  capillary;  4,  plasma 
in  capillary;  5,  red  blood  corpuscle. 


if  any  foreign  material  should 
get  into  the  windpipe  or  bron- 
chial tubes,  it  will  be  expelled 
by  the  action  of  the  cilia.  It 
is  by  means  of  cilia  that  phlegm 
is  raised  from  the  throat. 
Such  action  is  of  great  impor- 
tance as  it  prevents  the  filling 
of  the  air  passages  with  foreign 
matter.  The  bronchi  end  in 
very  minute  air  s.xs  called 
alveoli;  these  are  little  pouches 
having  elastic  walls.  It  is 
into  these  pouches  that  air  is 
taken  when  we  inspire  or  take 
a  deep  breath.  Thus  we  see 
the  lung  of  man  gets  a  very 


382 


HUMAN   PHYSIOLOGY 


great  increase  in  wall  area  by  having  a  large  number  of  tiny  sacs 
instead  of  one  large  one  as  in  the  frog.  In  the  walls  of  the  alveoli 
are  numerous  capillaries,  the  ends  of  arteries  which  pass  from 
the  heart  into  the  lung.  It  is  through  the  thin  walls  of  the  alveoli 
that  an  interchange  of  gases  takes  place  which  results  in  the  blood 
giving  up  part  of  its  load  of  carbon  dioxide,  and  taking  up  oxygen 
in  its  place. 

The  Pleura.  —  The  lungs  are  covered  with  a  thin  elastic  mem- 
brane, the  pleura.  This  forms  a  bag  in  which  the  lungs  are  hung. 
Between  the  walls  of  the  bag  and  the  lungs  is  a  space  filled  with 
lymph.  By  this  means,  the  lungs  are  prevented  from  rubbing 
against  the  walls  of  the  chest. 

Breathing.  —  In  every  full  breath  there  are  two  distinct  move- 
ments; inspiration  (taking  air  in)  and  expiration  (forcing  air  out). 
Thus  this  action  differs  considerably  from  "  breathing  "  movements 
of  the  frog.  The  frog  pumps  air  into  its  lungs  by  raising  and  lower- 
ing the  floor  of  the  mouth  and  then  shutting  the  flaps  or  valves  in 
the  anterior  nares.  It  is  actually  a  process  of  swallowing.  In  man 
the  act  of  inspiration  is  partly  under  the  control  of  the  will.  We 
are  able  to  take  a  long  breath,  or  a  short  breath,  though  we  can- 
not stop  breathing.  An  inspiration  is  produced  by  the  contrac- 
tion of  the  muscles  between  the  ribs  together  with  the  contraction 

of  the  diaphragm,  a  muscular  wall  just  below 
the  heart  and  lungs  (not  found  in  the  frog); 
this  results  in  pulling  down  the  diaphragm  and 
pulling  upward  and  outward  of  the  ribs,  thus 
making  the  space  within  the  chest  cavity 
larger.  The  lungs,  which  lie  within  this  cavity, 
are  filled  by  the  air  rushing  into  the  larger 
space  thus  made.  An  expiration  is  simpler 
than  an  inspiration  for  it  requires  no  muscular 
effort;  the  muscles  relax,  the  breastbone  and 
ribs  sink  into  place,  while  the  diaphragm  re- 
turns to  its  original  position. 


Apparatus  to  illustrate 
the  action  of  the  dia- 
phragm in  respira- 
tion. 


A  piece  of  apparatus  which  illustrates  to  a  de- 
gree the  mechanics  of  breathing  may  be  made  as 
follows :  Attach  a  string  to  the  middle  of  a  piece  of 
sheet  rubber.     Tie  the  rubber  over  the  large  end  of 


RESPIRATION  383 

a  bell  jar.  Pass  a  glass  tube  through  a  rubber  stopper.  Fasten  a  small 
toy  balloon  to  the  lower  end  of  the  tube.  Close  the  small  end  of  the  jar 
with  the  stopper.  Adjust  the  tube  so  that  the  balloon  shall  hang  free  in 
the  jar.  If  now  the  rubber  sheet  is  pulled  down  by  means  of  the  string,  the 
air  pressure  in  the  jar  is  reduced  and  the  toy  balloon  within  expands,  owing 
to  the  air  pressure  down  the  tube.  When  the  rubber  is  allowed  to  go 
back  to  its  former  position,  the  balloon  collapses. 

Coughing,  Sighing,  and  Sneezing.  —  Coughing  is  a  sudden  strong  ex- 
piration,  with  the  glottis  (or  top  of  the  windpipe)  closed.  A  sigh  is  a 
quick  inspiration  followed  by  a  quiet  expiration.  A  sneeze  is  a  sharp 
expiration,  the  air  passing  through  the  nose  because  the  passage  to  the 
mouth  is  closed  by  the  descent  of  the  soft  palate. 

Rate  of  Breathing  and  Amount  of  Air  Breathed.  —  During  quiet 
breathing,  the  rate  of  inspiration  is  from  fifteen  to  eighteen  times  per  minute; 
this  rate  largely  depends  on  the  amount  of  physical  work  performed.  About 
thirty  cubic  inches  of  air  are  taken  in  and  expelled  during  the  ordinary 
quiet  respiration.  The  air  so  breathed  is  called  tidal  air.  In  a  "long 
breath,"  we  take  in  about  100  cubic  inches  in  addition  to  the  tidal  air. 
This  is  called  complemental  air.  By  means  of  a  forced  expiration,  it  is 
possible  to  expel  from  75  to  100  cubic  inches  more  than  tidal  air;  this  air 
is  called  reserve  air.  What  remains  in  the  lungs,  amounting  to  about 
100  cubic  inches,  is  called  the  residual  air.  (See  diagram,  page  384.)  The 
value  of  deep  breathing  is  seen  by  a  glance  at  the  diagram.  It  is  only  by 
this  means  that  we  clear  the  lungs  of  the  reserve  air  with  its  accompanying 
load  of  carbon  dioxide. 

The  actual  amount  of  oxygen  used  in  the  body  during  the  course  of  a 
day  is  nearly  25  ounces;  this  being  almost  entirely  used  in  oxidizing  the 
food  materials  taken  into  the  body  during  the  24  hours. 

Respiration  under  Nervous  Control. — The  muscular  movements 
which  cause  an  inspiration  are  partly  under  the  control  of  the  will,  but  in 
part  the  movement  is  beyond  our  control.  The  nerve  centers  which  govern 
inspiration  are  part  of  the  sympathetic  nervous  system  of  which  we  shall 
learn  later.  That  the  sympathetic  nervous  system  controls  respiratory 
movements  is  seen,  for  example,  in  the  involuntary  short  breath  taken 
by  the  bather  who  plunges  into  cold  water.  Anything  of  an  irritating  nature 
in  the  trachea  or  larynx  will  cause  a  sudden  expiration  or  cough.  When  a 
boy  runs,  the  quickened  respiration  is  due  to  the  fact  that  oxygen  is  used 
up  rapidly  and  a  larger  quantity  of  carbon  dioxide  is  formed.  These  facts, 
together  with  the  presence  of  certain  other  poisonous  materials  in  the  lung 
cells,  stimulate  the  nervous  center  which  has  control  of  respiration  to  greater 
activity,  and  quickened  inspiration  follows. 

Experiments    to    determine   Changes   undergone   by   Air   in  the 
Lungs.  —  1.  Breathe  on  the  bulb  of  a  thermometer  and  record  any  changes 
2.    Breathe  gently  on  any  polished  glass  or  metal  surface.     Note  what 
happens. 


384 


HUMAN   PHYSIOLOGY 


3.  Take  a  moderate  breath,  and  force  air  (tidal  air)  through  hmewater. 
Notice  what  occurs. 

4.  Force  the  last  part  of  a  deep  expiration  (reserve  air)  through  lime- 
water.     Note  result.     What  is  one  reason  for  deep  breathing? 

Changes  in  Air  in  the  Lungs.  —  Air  is  much  warmer  after  leaving 
the  lungs  than  before  it  enters  them.  Expired  air  contains  a  con- 
siderable amount  of  moisture,  which  it  has  taken  up  in  the  air 

sacs  of  the  lungs.  The  presence  of  car- 
bon dioxide  may  easily  be  detected  in 
expired  air.  Air  such  as  we  breathe 
out  of  doors,  contains,  by  volume :  — 

Nitrogen 79.00 

Oxygen 20.90 

Carbon  dioxide 04 


Tidal  Air 
30  cu.  in. 


sResMtfM 


WO'O^ciG^iW. 


^30 
cu.  in. 


Air    expired   from    the    lungs,    con- 
tains :  — 

Nitrogen 79 

Oxj^gen 16 

Carbon  dioxide 4+ 


In  other  words,  there  is  a  loss  of  be- 
tween four  and  five  per  cent  oxygen, 
and  nearly  a  corresponding  gain  in  car- 
bon dioxide,  in  expired  air.  There  are 
also  some  other  organic  substances  pres- 
ent. The  volume  of  carbon  dioxide 
given  off  is  always  a  little  less  than  the 
amount  of  oxj^gen  taken  in.  This  seems 
to  show  that  some  ox^^gen  unites  with 
some  of  the  chemical  elements  in  the  body. 

Loss  FROM  THE  LuNGs.  —  A  man  expires  about  540  cubic  inches  of  air 
per  minute;  this  would  make  a  total  of  something  over  770,000  cubic  inches 
in  twenty-four  hours.  Of  this  air,  about  4  per  cent  is  carbon  dioxide,  the 
amount  varying  with  the  amount  and  kind  of  work  performed.  There 
would  be  at  least  31,000  cubic  inches  of  carbon  dioxide  expired  in  twenty- 
four  hours;  this  amount  weighs  nearly  thirty  ounces.  The  amount  of 
water  evaporated  by  the  lungs  in  twenty-four  hours  is  estimated  at  half 
a  pint,  so  the  lungs  are  a  source  of  actual  loss  in  body  weight. 


Diagram  showing  the  relative 
amounts  of  tidal,  comple- 
mental,  reserve,  and  residual 
air.  The  brace  shows  the 
average  lung  capacity  for  the 
adult  man. 


RESPIRATION 


385 


Changes  in  the  Blood  within  the  Lungs.  —  Blood,  after  leaving 
the  lungs,  is  much  brighter  red  than  just  before  entering  them. 
The  change  in  color  is  due  to  a  taking  up  of  oxygen  by  the  htcmo- 
globin  of  the  red  corpuscle.  Changes  taking  place  in  blood  are 
obviously  the  reverse  of  those  which  take  place  in  air  in  the  lungs. 
Blood  in  the  capillaries  within  the  lungs  gains  from  four  to  five 
per  cent  of  oxygen  which  the  air  loses.  At  the  same  time  blood  loses 
the  four  per  cent  of  carbon  dioxide  which  the  air  gains.  The  water 
given  off  is  mostly  lost  from  the  blood. 

Tissue  Respiration. — It  has  been  found,  in  the  case  of  ver>' 
,  simple  animals,  such  as  the  amoeba,  that  when  oxidation  takes  place 
in  a  cell,  work  or  release  of  heat  results  from  this  oxidation.  The 
oxygen  taken  into  the  lungs 
is  not  used  there,  but  is  car- 
ried by  the  blood  to  such 
parts  of  the  body  as  need 
oxygen  to  oxidize  food  mate- 
rials either  in  the  performance 
of  work  or  the  maintenance 
of  the  body  temperature. 
The  quantity  of  oxygen  used 
by  the  body  is  nearly  depend- 
ent on  the  amount  of  work 
performed.  From  twenty  to  twenty-five  ounces  is  taken  in  and 
used  by  the  body  every  day.  Oxygen  is  constantly  taken  from 
the  blood  by  tissues  in  a  state  of  rest.  This  ox3^gen  is  used  up 
when  the  body  is  at  work.  This  is  proved  by  the  fact  that  in  a 
given  time  a  man,  when  working,  gives  off  more  carbon  dioxide 
than  the  oxygen  he  has  taken  in  during  that  time. 

'^Alcohol  interferes  with  the  Respiration  of  the  Cells.  —  Alcohol 
is  quickly  absorbed  from  the  stomach  and  intestine  and  as  quickly 
disappears.  After  it  is  taken,  little  or  no  alcohol,  or  any  substance 
like  alcohol,  or  any  substance  containing  so  little  oxygen  as  alcohol, 
can  be  found  in  any  waste  of  the  body.  Hence  the  inference  is 
that  it  must  be  oxidized,  although  the  exact  point  and  the  manner 
of  its  oxidation  may  not  be  known.  But  the  evidence  for  its  oxi- 
dation is  the  same  as  that  for  the  oxidation  of  sugar. 

hunter's  BIOL.  —  25 


Diagram  to  show  the  respiration  of  cells. 


S86  HUMAN  PHYSIOLOGY 

"  Every  ounce  of  alcohol  requires  nearly  two  ounces  of  oxygen 
to  oxidize  it  fully.  Taking  twenty-five  ounces  of  oxygen  gas  as 
the  amount  used  in  a  day,  there  will  be  only  one  ounce  used  in  an 
hour.  So  to  oxidize  an  ounce  of  alcohol  takes  an  amount  of 
oxygen  equal  to  the  whole  supply  of  the  body  for  two  hours. 
Three  or  four  drinks  of  whisky  contain  this  ounce  of  alcohol. 
If  this  amount  is  drunk,  there  will  soon  be  a  lessened  action  and 
a  narcotic  effect  throughout  the  body,  due  mainly  to  the  lack  of 
oxygen.  A  noticeable  degree  of  uncertain  action  is  called  in- 
toxication. 

"  Using  alcohol  in  the  body  is  like  burning  kerosene  in  a  coal 
stove.  By  taking  great  care  a  little  kerosene  can  be  made  to  give 
out  some  heat  from  the  stove,  but  the  operation  is  dangerous. 
Some  people  seem  to  oxidize  alcohol  within  the  body  with  but 
Httle  harm;  but  they  run  great  risks  of  doing  themselves  harm, 
and  the  result  is  not  nearly  so  good  as  if  they  had  used  proper 
food. 

'^  Poisons  produced  by  Alcohol.  —  When  too  little  oxygen  enters 
the  draft  of  the  stove,  the  wood  is  burned  imperfectly,  and  there 
are  clouds  of  smoke  and  irritating  gases.  So,  if  oxygen  goes  to  the 
alcohol  and  too  little  reaches  the  cells,  instead  of  carbonic  acid 
gas,  and  water,  and  urea  being  formed,  there  are  other  products, 
some  of  which  are  exceedingly  poisonous  and  which  the  kidneys 
handle  with  difficulty.  The  poisons  retained  in  the  circulation 
never  fail  to  produce  their  poisonous  effects,  as  shown  by  head- 
aches, clouded  brain,  pain,  and  weakness  of  the  body.  The  word 
intoxication  means,  4n  a  state  of  poisoning.'  These  poisons  grad- 
ually accumulate  as  the  alcohol  takes  oxygen  from  the  cells. 
The  worst  effects  come  last,  when  the  brain  is  too  benumbed  to 
judge  fairly  of  their  harm.  It  is  not  true  that  alcohol  in  a  small 
amount  is  beneficial.  A  little  is  too  much,  if  it  takes  oxygen 
which  would  otherwise  be  available  to  oxidize  wholesome  food. 

"  Effects  of  Tobacco.  —  Tobacco  smoke  contains  the  same  kind 
of  poisons  as  the  tobacco,  with  other  irritating  substances  added. 
It  is  usually  sucked  into  the  mouth  and  at  once  blown  out  again, 
but  cigarette  smoke  is  commonly  drawn  into  the  lungs  and  after- 
wards blown  out  through  the  nose.     It  is  irritating  to  the  throat, 


RESPIRATION  387 

causing  a  cough  and  rendering  it  more  liable  to  inflammation. 
If  inhaled  into  the  bronchi,  it  produces  still  greater  irritation, 
and  the  vaporized  nicotine  is  more  readily  absorbed  as  the  smoke 
is  inhaled  the  more  deeply.  Cigarettes  contain  the  same  poisons 
as  other  forms  of  tobacco,  and  often  contain  other  poisons  which 
are  added  to  flavor  them."  —  Overton,  Applied  Physiology. 

Need  of  Ventilation.  —  During  the  course  of  a  day  the  lungs  have  lost 
to  the  surrounding  air  nearly  two  pounds  of  carbon  dioxide.  This  means  that 
about  three  fifths  of  a  cubic  foot  is  given  off  from  each  person  during  an 
hour.  When  we  are  confined  for  some  time  in  a  room,  it  becomes  neces- 
sary to  get  rid  of  this  carbon  dioxide.  This  can  be  done  only  by  means  of 
proper  ventilation.  Other  materials  are  passed  off  from  the  lungs,  with 
carbon  dioxide.  It  is  the  presence  of  these  wastes  in  combination  with 
carbon  dioxide  that  makes  breathed  air  particularly  unwholesome.  It  has 
been  determined  that  as  little  as  one  per  cent  carbon  dioxide  is  injurious  in 
expired  air,  although  a  much  greater  percentage  than  this  may  be  safely- 
breathed  if  the  carbon  dioxide  is  introduced  into  fresh  air.  The  presence  of 
impurities  in  the  air  of  a  room  may  easily  be  determined  by  its  odor.  The 
"close"  smell  of  a  poorly  ventilated  room  is  due  to  organic  impurities  given 
off  with  the  carbon  dioxide.  This,  fortunately,  gives  us  an  index  by  which 
we  may  prevent  poisoning.  Air  containing  8  parts  of  carbon  dioxide  to 
10,000  parts  of  air  is  bad;  while  from  12  to  14  parts  in  10,000  makes  a 
very  dangerous  amount.  Among  the  factors  which  take  oxygen  fro  in  the 
air  in  a  closed  room  and  produce  carbon  dioxide,  are  burning  gas  or  oil 
lamps,  stoves,  the  presence  of  a  number  of  people,  etc. 

Proper  Ventilation.  —  Ventilation  consists  in  the  removal  of 
air  that  has  been  used,  and  the  introduction  of  a  fresh  supply  to 
take  its  place.  If  we  remember  that  warm  air  is  lighter  than  cold 
air,  and  carbon  dioxide  is  heavier  than  air,  we  can  see  that  ventila- 
tion outlets  should  be  on  the  level  of  the  floor.  The  inlets  should 
be  near  the  top  of  the  room,  especially  in  houses  heated  by  any 
method  of  direct  radiation,  such  as  steam  or  hot  water.  A  good 
method  of  ventilation  for  the  home  is  obtained  by  placing  a  board 
two  or  three  inches  high  between  the  lower  sash  and  the  frame  of 
a  window. 

Sweeping  and  Dusting.  —  It  is  very  easy  to  demonstrate  the 
amount  of  dust  in  the  air  by  following  the  course  of  a  beam  of 
light  in  a  darkened  room.  We  have  already  proved  that  spores 
of  mold  and  yeast  exist  in  the  air.     That  bacteria  are  also  present 


388  HUMAN   PHYSIOLOGY 

can  be  proved  by  exposing  a  sterilized  gelatin  plate  to  the  air 
in  a  schoolroom  for  a  few  moments.^ 

Many  of  the  bacteria  present  in  the  air  are  active  in  causing 
diseases  of  the  respiratory  tract,  such  as  diphtheria,  membranous 
croup,  and  tuberculosis.  Other  diseases,  as  colds,  bronchitis, 
(inflammation  of  the  bronchial  tubes),  and  pneumonia  (inflam- 
mation of  the  tiny  air  sacs  of  the  lungs),  are  probably  caused  by 
bacteria. 

Dust,  with  its  load  of  bacteria,  will  settle  on  any  horizontal  sur- 
face in  a  room  not  used  for  three  or  four  hours.  Dusting  and 
sweeping  should  always  be  done  with  a  damp  cloth  or  broom, 
otherwise  the  bacteria  are  simply  stirred  up  and  sent  into  the  air 
again.  The  proper  watering  of  streets  before  they  are  swept  is 
also  an  important  factor  in  health. 

Ventilation  of  Sleeping  Rooms.  —  Sleeping  in  close  rooms  is 
the  cause  of  much  illness.  Beds  ought  to  be  placed  so  that  a 
constant  supply  of  fresh  air  is  given  without  a  direct  draft.  This 
may  often  be  managed  with  the  use  of  screens.  Bedroom  windows 
should  be  thrown  open  in  the  morning  to  allow  free  entrance  of  the 
sun  and  air,  bedclothes  washed  frequently,  sheets  and  pillow 
covers  often  changed.  Bedroom  furniture  should  be  simple,  and 
but  little  drapery  allowed. 

Hygienic  Habits  of  Breathing.  —  Every  one  ought  to  accustom 
himself  upon  going  into  the  open  air  to  inspire  slowly  and  deeply 
to  the  full  capacity  of  the  lungs.  A  slow  expiration  should  follow. 
Take  care  to  force  the  air  out.  Breathe  through  the  nose,  thus 
warming  the  air  you  inspire  before  it  enters  the  lungs  and  chills 
the  blood.  Repeat  this  exercise  several  times  every  day.  You  will 
thus  prevent  certain  of  the  air  sacs  which  are  not  often  used,  from 
becoming  hardened  and  permanently  closed. 

The  Relation  of  Tight  Clothing  to  Correct  Breathing.  —  It  is  im- 
possible to  breathe  correctly  unless  the  clothing  is  worn  loosely 
over  the  chest  and  abdomen.  Tight  corsets  and  tight  belts  prevent 
the  walls  of  the  chest  and  the  abdomen  from  pushing  outward  and 

*  Ex}3ose  two  sterilized  dishes  containing  culture  media ;  one  in  a  room  being 
swept  with  a  damp  broom  and  the  other  in  a  room  which  is  being  swept  in  the  usual 
manner.  Note  the  formation  of  colonies  of  bacteria  in  each  dish.  In  which 
dish  does  the  most  growth  take  place? 


RESPIRATION  389 

interfere  with  the  drawing  of  air  into  the  lungs.  They  may  also 
result  in  permanent  distortion  of  parts  of  the  skeleton  directly  under 
the  pressure.  Other  organs  of  the  body  cavity,  as  the  stomach  and 
intestines,  may  be  forced  downward,  out  of  place,  and  in  conse- 
quence do  not  perform  their  work  properly. 

Relation  of  Exercise.  —  We  have  already  seen  that  exercise  re- 
sults in  the  need  of  greater  food  supply,  and  hence  a  more  rapid 
pumping  of  blood  from  the  heart.  With  this,  comes  need  of  more 
oxygen  to  allow  the  oxidations  which  supply  the  greater  energy 
used.  Hence  deeper  breathing  during  time  of  exercise  is  a  prime 
necessity  in  order  to  increase  the  absorbing  surface  of  the  lungs. 

Suffocation  and  Artificial  Respiration.  —  Suffocation  results  from  the 
shutting  off  of  the  supply  of  oxygen  from  the  lungs.  It  may  be  brought 
about  by  an  obstruction  in  the  windpipe,  by  a  lack  of  oxygen  in  the  air,  by 
inhaling  some  other  gas  in  quantity,  or  by  drowning.  A  severe  electric 
shock  may  paralyze  the  nervous  centers  which  control  respiration,  thus 
causing  a  kind  of  suffocation.  In  all  the  above  cases,  death  may  be  pre- 
vented by  recourse,  in  time,  to  artificial  respiration.  To  accomplish  this 
place  the  patient  on  his  back  with  the  head  lower  than  the  body;  grasp  the 
arms  near  the  elbows  and  draw  them  upward  and  outward  until  they  are 
stretched  above  the  head,  on  a  line  with  the  body.  By  this  means,  the 
chest  cavity  is  enlarged  and  an  inspiration  produced.  To  produce  an  ex- 
piration, carry  the  arms  downward,  and  press  them  against  the  chest,  thus 
forcing  the  air  out  of  the  lungs.  This  exercise,  regularly  repeated  every  few 
seconds,  if  necessary  for  hours,  has  been  the  source  of  saving  many  lives. 

Effect  of  Alcohol  and  Tobacco  on  Respiration.  —  It  has  been 
shown  that  alcohol  tends  to  congest  the  membranes  of  the 
organs  of  respiration.  This  it  does  by  relaxing  the  membranes 
of  the  throat  and  lungs. 

"  Those  who  have  injured  themselves  with  alcohol  show  less 
power  of  resistance  against  influences  unfavorable  to  health, 
and  are  carried  off  by  diseases  which  other  people  of  the  same  age 
pass  through  safely,  especially  in  cases  of  inflammation  of  the 

lungs.'' BiRCH-HlRSCHFELD. 

'*  The  action  of  alcohol  upon  the  muscular  walls  of  the  arteries, 
which  has  been  already  more  than  once  referred  to,  is  especially 
important  in  the  capillaries  of  the  lungs.  When  they  are  dilated 
by  the  paralyzing  effect  of  alcohol,  their  expansion  reduces  the 


390  HUMAN   PHYSIOLOGY 

size  of  the  air  cells  in  the  lungs  and  leaves  less  room  for  the  air 
which  the  lungs  need,  so  that  less  oxygen  is  supplied  to  the  blood. 
When  the  capillaries  are  often  or  continuously  distended  in  this 
way,  their  walls  are  likely  to  become  permanently  thickened, 
and  the  interchange  of  gases  which  normally  takes  place  there, 
by  which  carbon  dioxide  passes  from  the  blood  while  the  purify- 
ing oxygen  is  taken  into  the  blood,  is  impeded.  Serious  disease 
even  may  result,  such  as  a  peculiar  and  quickly  fatal  form  of  con- 
sumption found  only  among  drinkers  of  alcohohc  fluids. 

"  The  throat,  bronchial  tubes,  and  lungs  of  a  tobacco  smoker 
are  all  hable  to  irritation  by  the  poisonous  smoke,  and  chronic  in- 
flammation is  often  caused.  The  nicotine  of  tobacco  is  a  deadly 
poison,  and  in  cigarettes  there  are  often  other  poisons  equally 
dangerous  to  health."  —  Macy,  Physiology. 

"  Dr.  Legendre,  a  Paris  physician,  has  recently  pubUshed,  for 
public  distribution,  a  leaflet  in  which  he  says:  'Alcohol  is  a  fre- 
quent cause  of  consumption  by  its  power  of  weakening  the  lungs. 
Every  year  we  see  patients  who  attend  the  hospital  for  alcoholism 
come  back  after  a  period  to  be  treated  for  consumption.' ''  —  Lon- 
don Lancet. 

''  An  American  medical  writer  (Journal  of  American  Medical 
Association)  points  out  the  reason  why  the  use  of  alcohol  makes 
one  hable  to  consumption.  He  mentions  the  use  of  alcohol  among 
various  other  things  which  cause  the  natural  vital  resistance  of 
the  healthy  body  to  be  impaired.  Among  those  other  things  men- 
tioned with  alcohol,  which  produce  this  impairment  of  vital  re- 
sistance, are  :  '  Living  in  overcrowded,  ill-ventilated  houses,  on 
damp  soils,  or  insufficient  clothing  and  outdoor  exercise.'  "  — 
Hall,  Elementary  Physiology. 

Tobacco  has  a  somewhat  similar  effect,  besides  causing  a  con- 
stant irritation  of  the  diseased  surfaces. 


XXXIV.     EXCRETION 

Organs  of  Excretion.  —  All  the  life  processes  which  take  place 
in  a  living  thing  result  ultimately  in  the  formation  of  organic 
wastes  within  the  body.  This  is  the  direct  outcome  of  the  processes 
we  call  oxidation.  In  the  one-celled  animals  we  find  the  outer 
layer  of  the  body  used  to  excrete  or  discharge  waste  materials. 
In  some  invertebrates,  coiled  tubes  called  nephridia  are  found, 
for  the  purpose  of  throwing  off  nitrogenous  waste.  In  the  verte- 
brate animals,  the  skin  and  kidneys  perform  this  function,  hence 
they  are  called  the  organs  of  excretion. 

Laboratory  Work  on  the  Urino-genital  System  of  the  Frog.  —  The  organs  of 
excretion  and  those  of  reproduction  are  closely  connected  in  the  frog,  and 
are  best  studied  together.  In  a  male  frog  from  which  the  digestive  tract 
has  been  carefully  removed,  the  kidneys  may  be  found  closely  attached  at 
the  dorsal  side  of  the  body  cavity.  They  are  red-brown  in  color.  How 
many  are  there  ?  What  is  their  general  shape  ?  The  ovoid  bodies,  lying 
directly  on  the  kidneys,  are  the  spermaries.  Notice  the  yellowish  finger- 
like bodies  just  anterior  to  the  spermaries.  These  are  the  so-called  fatty 
bodies;  their  function  is  not  exactly  known,  though  it  is  believed  that  they 
contain  a  reserve  supply  of  food.  Look  along  the  outer  edge  of  each  kidney 
for  tiny  white  tubes,  the  ureters,  which  connect  each  kidney  with  the  cloaca. 
Just  ventral  to  the  cloaca  is  the  urinary  bladder,  a  large  thin-walled 
bipartedsac;  this  is  also  connected  with  the  cloaca.  (The  bladder  is  fre- 
quently found  in  a  collapsed  condition.  It  is  easy  to  cut  it  away  uninten- 
tionally) . 

Draw  the  urino-genital  system  of  the  male  frog  (twice  natural  size),  show- 
ing as  many  parts  as  you  can. 

In  the  female  frog,  a  large  part  of  the  body  cavity,  especially  at  the  breed- 
ing season,  may  be  filled  by  the  ovary;  this  contains  a  great  number  of 
black  and  white  eggs,  which  may  easily  be  seen  through  its  very  delicate 
walls.  On  each  side  of  the  body  cavity,  posterior  to  the  ovary,  are  found 
two  long  and  much-twisted  tubes,  the  oviducts.  In  these  tubes,  the  eggs 
receive  a  jellylike  coat  which  protects  them  after  they  are  laid.  The  ovi- 
ducts are  connected  with  the  cloaca.  The  position  of  the  kidneys,  ureters, 
and  bladder  is  practically  the  same  as  in  the  male  frog. 

Draw  (twice  natural  size)  the  urino-genital  system  of  the  female  frog, 
showing  the  ovary  and  oviduct  on  one  side  removed.  Label  all  the  parts 
shown. 

Laboratory  Work  on  the  Kidney.  —  An  idea  of  the  internal  structure  of  the 
kidney  of  man  may  be  gained  by  examination  of  a  sheep's  kidney.  Get 
the  butcher  to  leave  the  mass  of  fat  around  the  kidney.  Of  what  use  might 
this  fat  be  ?     Notice,  after  removing  the  fat,  that  the  kidney  appears  to  be 

391 


392 


HUMAN   PHYSIOLOGY 


Suprarenal 

body 

Cortex 

Medulla 

z--^=i^Pvra  m  ids 


closely  wrapped  in  a  thin  coat  of  connective  tissue ;  this  is  called  the  capsule. 

Remove  the  kidney  from  this  capsule.     Notice  its  color  and  shape.     The 

depression  called  the  hilum  is  deeper  than 
the  corresponding  region  in  the  kidney 
bean.  The  hollow  tube  passing  out  from 
this  region  is  called  the  ureter.  Blood 
vessels  also  enter  and  leave  the  kidney 
at  the  hilum.  Cut  the  kidney  lengthwise 
into  halves.  Try  to  find  the  following 
regions :  (1)  The  outer  or  cortical  region; 
note  its  color;  (2)  The  inner  or  medul- 
lary layer;  this  layer  is  provided  with 
little  projections ;  these  are  the  pyramids 
of  Malpighi,  so  called  after  their  dis- 
coverer, Marcello  Malpighi,  a  celebrated 
Italian  physiologist;  (3)  the  cavity  or 
pelvis  of  the  kidney.  At  the  summit  of 
each  pyramid  is  a  small  opening  through 
which  escapes  into  the  pelvis  the  secretion 
formed  in  the  little  tubules  which  make 
up  the  substance  of  the  kidney.  Draw  a 
sheep's  kidney,  cut  lengthwise,  showing 
all  the  above  points. 


-Ureter 


Longitudinal  section  of  kidney. 


a 


The  Human  Kidney. — The  description  given  above  will  apply 
almost  exactly  to  the  kidney  of  man  except  for  the  size.  The 
human  kidney  is  about  four  inches  long,  two  and  one  half  inches 
wide,  and  one  inch  in  thickness.  Its 
color  is  dark  red.  If  you  examine  the 
structure  of  the  medulla  and  cortex  (see 
above)  under  the  compound  microscope, 
you  will  find  these  regions  to  be  com- 
posed of  a  vast  number  of  tiny  branched 
and  twisted  tubules.  The  outer  end  of 
these  tubules  open  into  the  pelvis;  the 
inner  end,  in  the  cortex,  forms  a  tiny 
closed  sac.  In  each  sac,  the  outer  wall 
of  the  tube  has  grown  inward  and  car- 
ried with  it  a  very  tiny  artery.  This 
artery  breaks  up  into  a  mass  of  capil- 
laries. These  capillaries,  in  turn,  unite 
to  'form  a  small  vein  as  they  leave 
the  little  sac.  Each  of  these  sacs  with 
its  contained  blood  vessels  is  called  a 
glomerulus. 


Diagram  of  kidney  circulation, 
showing  a  glomerulus  and 
tubule ;  a,  artery  bringing 
blood  to  part ;  b,  capillary 
bringing  blood  to  glomerulus; 
b',  vessel  continuing  with 
blood  to  tubule;  c,  vein;  t, 
tubule  ;   G,  glomerulus. 


EXCRETION  393 

Wastes  given  off  by  the  Blood  in  the  Kidney.  — In  the  glomerulus 
the  blood  loses  by  osmosis,  through  the  very  thin  walls  of  the 
capillaries,  first,  a  considerable  amoimt  of  water  (amounting  to 
nearly  three  pints  daily) ;  second,  a  nitrogenous  waste  material 
known  as  urea;  third,  salts  and  other  waste  organic  substances, 
uric  acid  among  them. 

These  waste  products,  together  with  the  water  containing  them,  are 
known  as  urine.  The  total  amount  of  nitrogenous  waste  leaving  the  body 
each  day  is  about  twenty  grains ;  this  is  nearly  all  accounted  for  in  the  urea 
passed  off  by  the  kidney,  as  urine  is  secreted  in  the  kidney.  It  is  passed 
through  the  ureter  to  the  urinary  bladder;  from  this  reservoir  it  is  passed 
out  of  the  body,  through  a  tube  called  the  urethra.  After  the  blood  has 
passed  through  the  glomeruli  of  the  kidney  it  is  purer  than  in  any  other 
place  ui  the  body,  because,  before  coming  to  the  kidney,  the  blood  lost  a 
large  part  of  its  burden  of  carbon  dioxide  in  the  lungs.  After  leaving  the 
kidney  it  has  lost  much  of  its  nitrogenous  waste.  So  dependent  is  the 
body  upon  the  excretion  of  its  poisonous  material  that,  in  cases  where  the 
kidneys  do  not  do  their  work  properly,  death  may  ensue  within  a  few  hours. 

* 

Effect  on  the  Kidneys.  —  It  is  said  that  alcohol  is  one  of  the 
greatest  causes  of  disease  in  the  kidneys.  The  forms  of  disease 
known  as  '*  fatty  degeneration  of  the  kidney  ''  and  "  Bright's 
disease  "  are  both  frequently  due  to  this  cause.  The  kidneys  are 
the  most  important  organs. for  the  removal  of  nitrogenous  waste. 

Alcohol  unites  more  easily  with  oxygen  than  most  other  food 
materials,  hence  it  takes  away  oxygen  that  would  otherwise  be 
used  in  oxidizing  these  foods.  Imperfect  oxidation  of  foods  causes 
the  development  and  retention  of  poisons  in  the  blood  which  it 
becomes  the  work  of  the  kidneys  to  remove.  If  the  kidneys 
become  overworked,  disease  will  occur.  Such  disease  is  likely  to 
make  itself  felt  as  rheumatism  or  gout,  both  of  which  are  believed 
to  be  due  to  waste  products  (poisons)  in  the  blood. 

''  Influence  of  Alcohol  upon  Excretion.  —  If  the  waste  sub- 
stances constantly  formed  in  the  body  are  not  promptly  removed, 
they  tend  to  poison  the  system.  When  the  organism  is  at  a  high 
level  of  health,  the  breaking  down  of  tissue  by  oxidation,  which 
produces  waste,  goes  on  rapidly  and  vigorously.  When  this  is 
retarded,  as  we  have  seen  it  to  be  when  alcohol  is  introduced  into 


394  HUMAN  PHYSIOLOGY 

the  circulation  and  uses  up  the  oxygen  which  should  be  applied 
to  the  oxidation  of  food,  then  the  weight  may  increase,  but  it  is 
by  the  retention  of  poisonous  matter  which  ought  to  be  removed. 
No  other  one  cause  creates  so  much  disease  of  the  kidneys  as  does 
the  use  of  alcohol.  Imperfect  oxidation  of  food  develops  poisons 
which  the  kidneys  are  overtaxed  to  remove.  This  may  be  caused 
by  eating  too  much,  or  by  eating  unwholesome  food,  or  too  much  of 
certain  kinds  of  food,  as  sugar  especially;  or  it  may  be  caused  by 
alcohol.  *  Fatty  degeneration  of  the  kidneys  '  is  a  frequent  result 
of  the  use  of  alcoholic  drinks.  The  cells  of  the  tissues  become  so 
altered,  also,  that  they  fail  to  act  normally  by  removing  only  the 
poisonous  substances,  and  they  allow  the  valuable  elements  in 
the  blood  to  be  drained  off  with  the  waste.  This  is  seen  in  the 
serious  disease  called  '  Bright's  disease  '  in  which  the  albumin 
which  is  necessary  to  health  is  excreted  by  the  kidneys."  —  Macy, 
Physiology. 

The  Effects  of  Alcohol  upon  the  Kidneys.  —  Dr.  McMichael,  in  the 
Dietetic  and  Hygienic  Gazette,  says,  ''  Alcohol  produces  disease 
of  the  liver  and  of  the  kidneys  because  these  glands  are  most  con- 
cerned in  the  throwing  out  of  any  poison,  and  are  always,  until 
they  are  deranged  in  structure,  engaged  in  removing  it  from  the 
body.'*  He  further  says  that  the  disease  almost  universally 
caused  in  the  liver  by  alcohol,  is  one  in  which  the  connective  tissue 
framework  of  the  liver  increases,  taking  the  place  of  the  liver  cells, 
until  the  liver  is  no  longer  able  to  perform  its  function. 

The  kidneys  may  undergo  a  change  similar  to  that  of  the  liver 
when  alcohol  is  used,  even  in  moderate  amounts,  for  a  long  period. 

The  Skin 

Structure  of  the  Skin.  —  In  man,  the  skin  is  composed  of  two 
layers,  an  outer  layer  called  the  epidermis,  and  an  inner  layer  called 
the  dermis.  The  outer  part  of  the  epidermis  is  composed  of 
flattened  dead  cells.  It  is  part  of  this  layer  that  peels  off  after 
sunburn,  or  that  separates  from  the  inner  part  of  the  epidermis 
when  a  water  blister  is  formed.  The  epidermis  frequently  forms 
callous  places  which  are  called  into  existence  by  much  use  of  the 


EXCRETION 


395 


exposed  part,  and  thus  form  pads  for  special  protection.  Such 
thickening  of  the  outer  layer  is  well  seen  in  the  pads  on  the  feet  of 
a  dog  or  cat.  The  inner  cells  of  the  epidermis  are  provided  with 
more  or  less  pigment  or  coloring  matter.  It  is  to  the  varying 
quantity  of  this  pigment  that  the  ''  light  or  dark "  complexion 
is  due.  The  inmost  layer  of  the  epidermis  is  made  up  of  small 
cells  which  are  constantly  dividing  to  form  new  cells  to  take  the 
place  of  those  in  the  outer  layer  which  are  lost. 


Sweat-Duct 


Sebaceous  Gland 


Horny  layer 
Pigment  layer 


Tactile  Organs' 
Nerve — 
Blood  Vessels - 


Sweat  Gland-zS^- 


Fat 


>  Epidermia 


'  Dermis 


Subcutaneous  layer 


Diagram  of  section  of  the  skin 


The  dermis  is  largely  composed  of  connective  tissue  filled  with 
a  network  of  blood  vessels  and  nerv^es.  This  layer  contains  the 
sweat  glands,  some  of  the  most  important  glands  in  the  body. 
Other  organs  connected  with  the  nervous  system  and  called  the 
tactile  corpuscles,  cause  this  part  of  the  skin  to  be  sensitive  to 
touch.  ' 

Nails.  —  Nails  are  a  development  from  the  horny  layer  of  the 
epidermis.  Except  at  the  tip,  the  nail  lies  directly  on  the  dermis, 
and  gets  its  pink  color  from  the  blood  beneath  it.  Nails  grow 
from  a  layer  of  living  cells  at  their  roots,  part  of  the  inner  layer 
of  the  epidermis. 

Hairs.  —  A  hair  is  also  an  outgrowth  of  the  horny  layer,  although 
it  is  formed  in  a  deep  pit  or  depression  in  the  dermis;  this  pit  is 


396  HUMAN   PHYSIOLOGY 

called  the  hair  follicle.  A  hair  is  formed  by  the  rapid  multiplica- 
tion of  the  cells  covering  a  little  projection  of  the  epidermis  at 
the  bottom  of  the  pit.  Scattered  through  the  dermis,  but  always 
connected  with  the  hair  follicles,  are  tiny  oil-secreting  glands,  the 
sebaceous  glands.  The  function  of  the  sebaceous  gland  is  to  keep 
the  hair  and  surface  of  the  skin  soft.  The  scales  of  fishes  and 
snakes,  the  feathers  of  birds,  and  the  hoofs  and  horns  of  cattle, 
are  all  examples  of  outgrowth  from  the  epidermis.  They  may 
then  be  considered  as  modifications  of  hair  or  nails. 

Structure  and  Use  of  Sweat  Glands. — Examine  the  surface  of 
your  skin  with  a  lens.  Notice  the  surface  is  thrown  into  little  ridges. 
In  these  ridges  may  be  found  a  large  number  of  very  tiny  pits; 
these  are  the  pores  or  openings  of  the  sweat-secreting  glands. 
From  each  opening  a  little  tube  penetrates  deep  within  the  epider- 
mis; there,  coiling  around  upon  itself  several  times,  it  forms  the 
sweat  gland.  Close  around  this  coiled  tube  are  found  many  capil- 
laries. From  the  blood  in  these  capillaries,  cells  lining  the  wall 
of  the  gland  tube  take  water,  and  with  it  a  little  carbon  dioxide, 
urea,  and  some  salts  (table  salt  among  others).  This  forms 
the  excretion  known  as  sweat.  It  has  been  estimated  that  there 
are  over  two  million  five  hundred  thousand  sweat  glands  in  the 
skin  of  an  average-sized  person.  A  combined  secretion  from  these 
glands  amounts  normally  to  a  little  over  a  pint  during  twenty-four 
hours.  The  amount  secreted  varies  greatly.  At  all  times,  a  small 
amount  of  sweat  is  given  off,  but  this  is  evaporated  or  is  absorbed 
by  the  underwear;  as  it  passes  off  unnoticed  it  is  called  insen- 
sible perspiration.  In  hot  weather  or  after  hard  manual  labor 
the  amount  of  perspiration  is  greatly  increased. 

Home  or  Laboratory  Experiment.  —  Take  your  temperature  by  inserting  a 
clinical  thermometer  in  the  mouth  just  under  the  tongue  immediately  before 
and  immediately  after  some  hard  manual  labor.  Note  the  difference  in 
temperature  if  any. 

Relation  of  Bodily  Heat  to  Work  Performed.  — The  bodily  tem- 
perature of  a  man  engaged  in  manual  labor  will  be  found  to  be 
but  little  higher  than  his  temperature  when  at  rest.  When  a 
man  works,  he  releases  energy  by  oxidizing  food  material  or  tissue 
in  the  body.     Thus  we  know  from  our  previous  experiments  that 


EXCRETION  397 

heat  is  released.  Muscles,  nearly  one  half  the  weight  of  the  body, 
release  about  five  sixths  of  their  energy  as  heat.  At  all  times, 
they  are  giving  up  some  heat.  How  is  it,  then,  that  the  bodily 
temperature  does  not  differ  greatly  at  such  times? 

Regulation  of  Heat  of  the  Body.  —  The  temperature  of  the  body 
is  largely  regulated  by  means  of  the  activity  of  the  sweat  glands. 
If  a  large  amount  of  perspiration  is  produced,  it  takes  a  correspond- 
ingly large  amount  of  heat  to  evaporate  it.  Thus  it  is  that  when  we 
perspire,  we  are  cooler  afterward.  The  object  of  increased  per- 
spiration, then,  is  to  remove  heat  from  the  body.  In  hot  weather, 
the  blood  vessels  of  the  skin  are  dilated ;  in  cold  weather,  they  are 
made  smaller  by  the  action  of  the  nei'vous  system. 

With  a  large  amount  of  blood  present  in  the  skin,  perspiration 
is  increased;  with  a  small  amount,  it  is  diminished.  Hence,  we 
have  in  the  skin  an  automatic  regulator  of  bodily  temperature. 
Bodily  temperature  is  also  helped  to  be  kept  at  a  constant  level,  be- 
cause the  amount  of  heat  produced  in  the  body  is,  to  some  extent, 
regulated  by  the  temperature  outside  of  the  body.  Cold  air 
stimulates  the  body  to  produce  more  heat.  A  high  temperature 
outside  the  body  retards  its  heat  production. 

Sweat  Glands  under  Nervous  Control.  —  The  sweat  glands,  like  the 
other  glands  in  the  body,  are  under  the  control  of  the  sympathetic  nervous 
system.  Frequently  the  nerves  dilate  the  blood  vessels  of  the  skin,  thus 
helping  the  sweat  glands  to  secrete,  by  giving  them  more  blood. 

"Thus  regulation  is  carried  out  by  the  nervous  system  determining,  on 
the  one  hand,  the  loss  by  governing  the  supply  of  blood  to  the  skin  and  the 
action  of  the  sweat  glands;  and  on  the  other,  the  production  by  diminish- 
ing or  increasing  the  oxidation  of  the  tissues."  —  Foster  and  Shore,  Physi- 
ology} 

Comparison  with  Cold-blooded  Animals.  —  We  have  seen  the  bodily 
temperature  of  a  frog  remain  nearly  that  of  the  surrounding  medium. 
Fishes,  all  amphibious  animals,  and  reptiles  are  alike  in  this  respect.     This 

*  "Some  warm-blooded  animals,  as  bears,  hiherjiate,  that  is,  sleep  all  through 
the  winter  and  take  no  food.  They  feed  well  in  the  warm  weather,  and  are  quite 
fat  at  the  close  of  autumn,  when  they  seek  some  sheltered  place  to  winter  in.  This 
shelter  and  their  warm,  furry  coats  make  the  loss  of  heat  very  little;  the  aniraal, 
except  for  its  breathing  and  the  beat  of  its  heart,  hardly  ever  moves  during  the 
winter,  and  even  those  necessary  movements  are  reduced  to  the  fewest  possible, 
the  breathing  and  heart  beat  being  much  slower  than  during  the  summer.  With 
return  of  warm  weather  the  creature  wakes  up  again,  but  is  then  lean  and  weak, 
having  burnt  up  its  fat  and  part  of  its  muscles  during  its  winter  sleep."  —  MartiNj 
The  Human  Body. 


398  HUMAN   PHYSIOLOGY 

change  in  the  bodily  temperature  is  due  to  the  absence  of  regulation  by  the 
nervous  system.  A  sort  of  regulation  is  exerted,  however,  by  outside  forces, 
for  the  cold  in  winter  causes  the  cold-blooded  animals  to  become  inactive. 
Warm  weather,  on  the  other  hand,  stimulates  them  to  greater  activity  and 
to  increased  oxidation.  This  is  naturally  followed  by  a  rise  in  bodily  tem- 
perature. 

Importance  of  Cleanliness  and  Proper  Clothing. — The  skin  as 
an  organ  of  excretion  is  of  importance.  It  is  of  even  greater  im- 
portance as  a  regulator  of  bodily  temperature.  The  mouths  of  the 
sweat  glands  must  not  be  allowed  to  become  clogged  with  dirt. 
The  skin  of  the  entire  body  should,  if  possible,  be  bathed  daily. 
For  those  who  can  stand  it,  a  cold  sponge  bath  is  best.  Soap 
should  be  used  daily  on  parts  exposed  to  dirt.  Exercise  in  the  open 
air  is  important  to  all  who  desire  a  good  complexion.  The  body 
should  be  kept  at  an  even  temperature  by  the  use  of  proper  under- 
clothing. Wool,  a  poor  conductor  of  heat,  should  be  used  in 
winter,  and  cotton,  which  allows  of  a  free  escape  of  heat,  in  summer. 

Cuts,  Bruises,  and  Burns. — In  case  the  skin  is  badly  broken, 
some  antiseptic  solution  (weak  carbolic  acid  or  mercuric  chloride 
tablets)  can  be  obtained  at  any  drug  store,  and  should  be  kept 
in  the  house.  N.B.  These  are  strong  poisons  and  should  be  used 
with  great  care  according  to  exact  directions.  This  solution  may 
be  applied  at  once.  Thus  bacteria  will  be  prevented  from  obtain- 
ing entrance  to  the  wound  and  causing  inflammation. 

"A  burn  or  scald  should  be  covered  at  once  with  a  paste  of 
baking  soda,  which  tends  to  lessen  the  pain  by  keeping  out  the 
air  and  reducing  the  inflammation.  A  mixture  of  linseed  oil  and 
lime  water,  known  as  carron  oil,  is  a  good  remedy  to  keep  on  hand 
for  burns.''  —  Peabody,  Physiology. 

'^  The  Bodily  Heat  as  affected  by  Alcohol.  —  The  paralyzing 
effect  of  the  use  of  alcoholic  drinks,  upon  the  muscles  in  the  walls 
of  the  minute  blood  vessels,  has  been  mentioned  in  connection 
with  the  muscles,  the  circulation,  and  respiration.  It  should  be 
referred  to  also  in  connection  with  the  subject  of  this  chapter. 

''  Because  alcohol  is  quickly  oxidized,  and  because  heat  is 
produced  in  the  process,  it  was  long  believed  to  be  of  value  in 
maintaining  the  heat  of  the  body.     A  different  view  now  prevails 


EXCRETION  399 

as  the  result  of  much  observation  and  experiment.  Travelers 
in  Arctic  regions  and  others  exposed  to  intense  cold  agree  that 
those  who  use  no  alcohol  whatever  are  far  better  able  to  resist 
+he  cold  than  are  those  who  indulge  in  it.  Physiologists  show  by 
careful  experiments  that  though  the  temperature  of  the  body  rises 
during  digestion  of  food,  it  is  lowered  for  some  hours  when  alcohol 
is  taken.  The  flush  which  is  felt  upon  the  skin  after  a  drink  of 
wine  or  spirits  is  due  in  part  to  an  increase  of  heat  in  the  body, 
but  also  to  the  paralyzing  effect  of  the  alcohol  upon  the  capillary 
walls,  allowing  them  to  dilate,  and  so  permitting  more  of  the  warm 
blood  of  the  interior  of  the  body  to  reach  the  surface.  There  it  is 
cooled  by  radiation,  and  the  general  temperature  is  lowered."  — 
Macy,  Physiology. 

Effect  of  Alcohol.  —  Alcohol  lowers  the  temperature  of  the  body 
by  dilating  the  blood  vessels  of  the  skin.  It  does  this  by  means  of 
its  influence  on  the  nervous  system.  It  is,  therefore,  a  mistake 
to  drink  alcoholic  beverages  when  one  is  extremely  cold,  because 
by  means  of  this  more  bodily  heat  is  allowed  to  escape. 

"  Alcohol  and  Heat.  —  The  amount  of  heat  in  the  body  depends 
upon  the  balance  between  its  production  and  its  loss.  The  rapid 
destruction  of  alcohol,  in  all  probability,  yields  heat  too  rapidly 
to  be  utilized  by  the  body.  The  most  constant  effect  of  taking 
alcohol  is  to  dilate  the  arteries  of  the  skin,  so  that  an' extra  amount 
of  heat  is  lost.  More  heat  is  always  lost  than  is  produced.  Alcohol 
lessens  the  power  of  the  body  to  endure  cold.  On  a  cold  day  when 
the  arteries  of  the  skin  are  contracted  so  that  there  is  but  little 
blood  to  warm  its  nerves,  alcohol  may  send  the  blood  to  these 
nerves  and  produce  an  agreeable  sense  of  warmth,  but  in  reality 
this  feeling  of  warmth  is  due  only  to  the  heat  which  is  passing  off 
from  the  interior  of  the  body."  —  Overton,  Applied  Physiology. 


XXXV.     THE   NERVOUS   SYSTEM 

General  Functions  of  the  Nervous  System.  —  We  have  seen  that, 
in  the  simplest  of  animals,  one  cell  performs  the  functions  neces- 
sary to  its  existence.  In  the  more  complex  animals,  where  groups 
of  cells  form  tissues,  each  having  a  different  function,  a  ner- 
vous system  is  developed.  The  functions  of  the  nervous  system  are: 
(1)  the  providing  of  the  man  with  sensation,  by  means  of  which  he  gets 
in  touch  with  the  world  about  him;  (2)  the  giving  to  the  human  being 
a  will,  a  provision  for  thought;  (3)  the  connection  of  organs  in  different 
parts  of  the  body  so  that  they  act  as  a  united  and  harmonious  whole. 
Cooperation  in  word  and  deed  is  the  end  attained.  We  are  all 
familiar  with  examples  of  the  cooperation  of  organs.  You  see 
food;  the  thought  comes  that  it  is  good  to  eat;  you  reach  out,  take 
it,  raise  it  to  the  mouth;  the  jaws  move  in  response  to  your  will; 
the  food  is  chewed  and  swallowed;  while  digestion  and  absorption 
of  the  food  are  taking  place,  the  nervous  system  is  still  in  control. 
The  nervous  system  also  regulates  pumping  of  blood  over  the  body, 
respiration,  secretion  of  glands,  and,  indeed,  ever\^  bodily  function. 

Divisions  of  the  Nervous  System.  —  The  control  of  a  number  of 
activities  for  the  attainment  of  a  definite  end  is  the  function  of  the 
nervous  system  in  the  lowest  as  well  as  the  highest  of  animals. 
In  the  vertebrate  animals,  the  nervous  system  consists  of  two 
divisions.  One  includes  the  brain,  spinal  cord,  the  cranial  and 
spinal  nerves,  which  together  make  up  the  cerebrospinal  nervous 
system.  The  other  division  is  called  the  sympathetic  nervous  sys- 
tem. The  activities  of  the  body  are  controlled  from  nen^e  centers 
by  means  of  fibers  which  extend  to  all  parts  of  the  body,  there 
ending  in  the  muscles.  The  brain  and  spinal  cord  are  examples 
of  such  centers,  since  they  are  largely  made  up  of  nerve  cells. 
Small  collections  of  nerve  cells,  called  ganglia,  are  found  in  other 
parts  of  the  body.  These  nerve  centers  are  connected,  to  a  greater 
or  less  degree,  with  the  surface  of  the  body  by  the  nerves  which 

400 


The  central  cerebro-spinal  nervous  system. 


401 


402 


HUMAN   PHYSIOLOGY 


A  nerve  cell  from  the  brain  of  a  mon- 
key, showing  a  great  number  of 
dendrites. 


serve  as  pathways  between  the  end  organs  of  touch,  sight,  taste, 
etc.,  and  the  centers  in  the  brain  or  spinal  cord.  Thus  sensation 
is  obtained. 

Nerve  Cells  and  Fibers.  —  A  nerve  cell,  like  most  other  cells  in  the  body, 
is  a  mass  of  protoplasm  containing  a  nucleus.     The  body  of  the  nerve  cell  is 

usually  rather  irregular  in  shape,  and  dis- 
tinguished from  most  other  cells  by  pos- 
sessing several  delicate,  branched  proto- 
plasmic projections  called  dendrites. 
(See  figure.)  One  of  these  processes,  the 
axis  cylinder  process,  is  much  longer  than 
the  others  and  ends  in  a  muscle  or  organ 
of  sensation.  The  axis  cylinder  process 
forms  the  pathway  over  which  nervous 
impulses  travel  to  and  from  the  nerve 
centers. 

Nerves  consist  of  bundles  of  such  tiny 
axis  C3dinder  processes,  bound  together  by 
connective  tissue.  As  a  nerve  ganglia  is 
a  center  of  activity  in  the  nervous  sys- 
tem, so  a  nerve  cell  is  a  center  of  activity 
which  may  send  an  impulse  over  this  thin  strand  of  protoplasm,  the  axis 
cjdinder  process,  prolonged  into  a  nerve  fiber  many  hundreds  of  thousands 
of  times  the  length  of  the  cell.  Some  nerve  cells  in  the  human  body,  al- 
though visible  only  under  the  compound  microscope,  give  rise  to  axis  cylin- 
der processes  several  feet  in  length.  Because  some  nerve  fibers  originate 
in  organs  that  receive  sensations  and  send  those  sensations  to  the  central 
nervous  system,  they  are  called  sensory  nerves.  Other  axis  cylinder  pro- 
cesses originate  in  the  central  nervous  system  and  pass  outward  as  nerve 
fibers;  such  nerves  produce  movement  of  muscles  and  are  called  motor  nerves. 

The  Cerebrospinal  Nervous  System  of  the  Frog. — For  this  exercise  use  frogs 
that  have  been  preserved  in  alcohol.  Those  previously  used  for  other  work 
on  the  anatomy  of  the  frog  will  do  perfectly  well. 

With  a  sharp  knife  or  scalpel,  cut  away  the  skin  from  the  top  of  the  head 
and  along  the  back.  Cut  carefully  through  the  top  of  the  cartilaginous 
skull.  The  brain  will  then  be  exposed,  lying  in  a  bony  cavity  surrounded 
by  a  watery  fluid,  the  function  of  which  is  to  protect  the  delicate  brain  from 
shock.  Notice  the  white  elongated  hemispheres  of  the  forehrain  or  cerebrum. 
The  two  anterior  projections  of  the  cerebrum  are  called  the  olfactory  lobes. 
It  is  by  means  of  the  olfactory  lobes  that  odors  are  perceived.  Posterior 
to  the  cerebrum  and  connected  with  it  is  the  midbrain.  The  dorsal  side  is 
enlarged  to  form  a  pair  of  optic  lobes.  How  do  the  optic  lobes  compare  in 
size  with  the  cerebrum  ?  Insert  the  blunt  end  of  a  scalpel,  and  turn  the  optic 
lobes  slightly  so  as  to  find  the  optic  nerves.  Notice  that  they  cross  each 
other,  the  one  from  the  right  optic  lobe  going  to  the  left  eyeball,  the  one 


THE  NERVOUS  SYSTEM 


403 


\/  -^DendHteM 

J  Cell  Bodf 


\xiH  Ct/Huiltr 


Procent 


from  the  left  optic  lobs  to  the  right  eyeball.  This  rroRsing  of  the  optic 
nerves  is  found  in  man  The  region  just  under  and  behind  the  optic  lobes 
is  the  hindhrain;  it  consists  of  the  cerebellum  (seen  as  a  little  ridge  post^irior 
to  the  optic  lobes)  and  the  medulla  (the  hindmost  part 
of  the  brain).  Notice  the  nerves  leaving  it  laterally. 
By  carefully  removing  the  bone  surrounding  the  spinal 
cord,  you  may  be  able  to  see  some  of  the  spinal  nerves 
and  the  cord  itself.  Make  a  drawing  of  the  brain  of 
the  frog,  naming  all  the  parts.  Now  turn  the  frog 
over.  After  removing  all  the  organs  from  the  body 
cavity,  trace  the  course  of  some  of  the  white  spinal 
nerves.  There  are  ten  in  all.  They  leave  the  spinal 
cord  by  two  branches  known  as  the  dorsal  and  ven- 
tral roots.  These  roots  unite  under  a  series  of  yellow- 
ish white  patches  {ganglionic  glands).  The  dorsal 
roots  enter  collections  of  nerve  cells  known  as  the 
spinal  ganglia.  Connected  with  that  part  of  the  cen- 
tral nervous  system  just  described  is  the  sympathetic 
nervous  system.  Part  of  this  may,  in  favorable  speci- 
mens, be  found  as  a  row  of  nerves  and  ganglia  lying 
along  each  side  of  the  spinal  cord  in  the  body  cavity. 
The  sympathetic  nervous  system  supplies  all  the  or- 
gans of  the  body  cavity,  and  is  connected  with  the 
spinal  and  cranial  (brain)  nerves.  In  man  the  sym- 
pathetic nervous  system  has  practically  the  same  posi- 
tion and  function  as  it  has  in  the  frog.  It  has  the 
control  of  the  organs  of  digestion,  circulation,  respira- 
tion, excretion,  and  reproduction,  the  so-called  vege- 
tative functions. 

Functions  of  the  Parts  of  the  Central  Ner- 
vous System  of  the  Frog.  —  From  careful  study  of 
living  frogs,  birds,  and  some  mammals  we  have  learned 
much  of  what  we  know  of  the  functions  of  the  parts 
of  the  central  nervous  system  in  man. 

It  has  been  found  that  if  the  entire  brain  of  a  frog  is  destroyed  and 
separated  from  the  spinal  cord,  "the  frog  will  continue  to  live  but  with  a 
very  peculiarly  modified  activity."  It  does  not  appear  to  breathe  nor  does 
it  swallow.  It  will  not  move  or  croak,  but  if  acid  be  placed  upon  the  skin 
so  as  to  irritate  it,  the  legs  make  movements  to  push  away  and  to  clean  off 
the  irritating  substance.  The  spinal  cord  is  thus  shown  to  be  a  center  for 
defensive  movements.  If  the  forebrain  be  separated  from  the  rest  of  the 
nervous  system,  the  frog  seems  to  act  a  little  differently  from  the  norinal 
animal.  It  jumps  when  touched  and  swims  when  placed  in  water.  It  will 
croak  when  stroked  or  swallow  if  food  be  placed  in  its  mouth.  Hut  it 
manifests  no  hunger  or  fear,  and  is  in  every  sense  a  machine  which  will 
perform  certain  actions  after  certain  stimulations.  Its  lnoveInent^s  arc 
automatic.  If  now  we  watch  the  movements  of  a  frog  which  has  the  brain 
uninjured  in  any  way,  we  find  that  the  frog  acts  spontaneously.  It  tries  to 
escape  when  caught.  It  feels  hungry  and  seeks  food.  It  is  capable  of 
voluntary  action      It  acts  like  a  normal  individual. 


Kervf-^ndM 


Diagram  of  a  iiouron  or 
nerve  unit. 


404 


HUMAN   PHYSIOLOGY 


The  Brain  of  Man.  —  In  man,  as  in  the  frog,  the  central  nervous 
system  consists  of  a  brain  and  spinal  cord  inclosed  in  a  bony  case 
with  the  nerves  leaving^  it.  From  the  brain,  twelve  pairs  of  nerves 
are  given  off;  thirty-one  more  leave  the  spinal  cord.  Along  the 
course  of  some  of  these  nerves  are  found  ganglia.  The  brain  has 
three  divisions.  The  cerebrum  makes  up  the  largest  part.  In  this 
respect  it  differs  from  the  cerebrum  of  the  frog  and  other  verte- 
brates. It  is  divided  into  two  lobes,  the  hemispheres,  which  are 
connected  with  each  other  by  a  broad  band  of  nerve  fibers.     The 


Cerebrum 


Cerebellum  — 


Medulla 


The  brain,  with  parts  separated  to  show  each  clearly. 


outer  surface  of  the  cerebrum  is  thrown  into  folds  or  convolutions. 
The  outer  layer,  seen  in  section,  is  gray  in  color,  made  up  of  nerve 
cells  and  supporting  material  (the  neuroglia,  a  kind  of  connective 
tissue).  The  inner  part  (white  in  color)  is  composed  largely  of 
fibers  which  pass  to  other  parts  of  the  brain  and  down  into  the 
spinal  cord.  (In  man,  the  midbrain  is  covered  by  the  cerebrum, 
and  need  not  be  considered  in  this  description.)  Under  the 
cerebrum,  and  dorsal  to  it,  lies  the  little  brain,  or  cerebellum,  a 
part  of  the  hindbrain.  This  part  consists  of  nerve  cells  and  fibers. 
The  two  sides  of  the  cerebellum  are  connected  by  a  band  of  nerve 


THE  NERVObiS  iSVSTJOM  405 

fibers  which  run  around  into  the  lower  hind])rain  or  medull-i  This 
band  of  fibers  is  called  the  pons.  The  medulla  is,  in  structure 
part  of  the  spinal  cord,  and  is  made  up  lar^rdy  of  fibers  runninJ 
longitudmally.  Just  above  the  pons,  these  fil.ers  are  collected  into 
two  bundles  which  separate  and  pass  up,  one  to  each  hemisphere 
of  the  cerebrum.     The  bundles  are  called  the  crura  cerebri 

Sensory  and  Motor  Nerve  Fibers.  —  Nerves  which  are  connected 
with  the  central  nervous  system  may  be  made  up  of  fibers  bearine; 


Face 

Sensory 

Face — 
Motor 

Tovigue 


nd 

Spinal  Nerves 


Heart    \ 

Lungs      \ 

Stomach     1 

Liver      J 


Diagram  of  the  distribution  of  the  cranial  nerves. 

sensations  from  the  skin  or  sense  organs  to  the  central  nen-ous 
system,  the  sensory  fibers,  or  of  other  fibers  which  carry  impulses 
from  the  central  nervous  system  to  the  outside,  the  motor  fibers. 
Some  nerves  are  made  up  of  both  kinds  of  fibers,  in  which  ciise  they 
are  called  mixed  nerves. 

Distribution  of  Cranial  (Brain)  Nerves  in  Frog  and  Man.  —  In 
the  frog,  the  cranial  nerves  agree  in  function  with  the  tirst  ten 
nerves,  or  cranial  nerves,  of  man.  There  are  t\f  o  additional  cranial 
nerves,  however,  found  in  man.  These  nerves  are  distributed  a.*? 
shown  in  the  table  on  the  following  page. 


406 


HUMAN   PHYSIOLOGY 


No.  OF 

Nerve 

Kind  of  Nerve 

Frog 

OR  Composi- 
tion OF  Nerve 

Man 

I 

Olfactory — to  nose 

Sensory 

Olfactory  —  to  nose 

II 

Optic  —  to  eye 

Sensory 

Optic  —  to  eye 

III  IV  VI 

To  muscles  of  eye 

Motor 

To  muscles  of  eye 

V 

To    tongue,    skin,   mus- 

Mixed 

To  tongue,  skin,  muscles 

cles  of  jaw 

of  jaw- 

VII 

To  muscles  of  face 

Motor 

To  muscles  of  face  and 
scalp 

VIII 

Auditory  —  to  ear 

Sensory 

Auditory  —  to  ear 

IX 

To  tongue  and  pharynx 

Mixed 

To  sense  organs  of 
tongue,  muscles  and 
throat 

X 

Vagus  —  to    lungs,     air 

Mixed 

To    organs    of    respira- 

passages, heart,  blood 

tion,     digestion,     etc.. 

vessels,  digestive  tract, 

movement     of     same. 

reproductive  organs 

Sensations  of  pain, 
hunger,  etc. 

XI 

Motor 

To  muscles  of  shoulder 

XII 

Motor 

To  muscles  of  tongue 

The  Sympathetic  Nervous  System.  —  The  sympathetic  nervous  system 
consists  of  a  series  of  ganglia  connected  with  each  other  and  with  the  cen- 
tral nervous  system  through  some  of  the  spinal  and  cranial  nerves,  especially 
the  vagus  (tenth  cranial).  The  sympathetic  system,  both  in  the  frog  and 
man,  controls  the  muscles  of  the  digestive  tract  and  blood  vessels,  the 
secretion  of  gland  cells  and  all  functions  which  have  to  do  with  life  processes 
in  the  body. 

Functions  of  the  Cerebrum.  —  In  general,  the  functions  of  the 
different  parts  of  the  brain  in  man  agree  with  those  functions 
we  have  already  observed  in  the  frog.  T'he  cerebrum  has  to  do 
with  conscious  activity,  that  is,  thought.  It  presides  over  what 
we  call  our  thoughts,  our  will,  and  our  sensations.  Each  part 
of  the  area  of  the  outer  layer  of  the  cerebrum  is  given  over 
to  some  one  of  the  different  functions  of  speech,  hearing, 
sight,  touch,  movements  of  bodily  parts.  The  movement  of 
the  smallest  part  of  the  body  has  its  definite  localized  center  in 
the  cerebrum.     Experiments  have  been  performed  on  monkeys, 


THE  NERVOUS  SYSTEM 


407 


and  these,  together  with  observations  made  on  persons  who  had 
lost  the  power  of  movement  of  certain  parts  of  the  hodv,  and  who, 
after  death,  were  found  to  have  had  diseases  localized  in  certain' 
parts  of  the  cerebrum,  have  given  to  us  our  knowledge  on  this  sub- 
ject. 

Reflex  Actions,  their  Meaning.  —  If  through  disease  or  for  other 
reasons  the  cerebrum  does  not  function,  no  will  power  is  exerted, 
no  intelligent  acts  per- 
formed,   and    no     in-  ^al^^B^^^ 
coming    impulses    are 
received  as  sensations. 
All  acts  performed  in 
such  a  state  are  known 
as    rejiex  actions.     An 
example    of    a    reflex 
may    be    obtained   by 
crossing  the   legs  and 
hitting  the  knee  a  sharp 
blow.     The  leg,  below 
the  knee,  will  fly  up  as 
a  result  of  reflex  stimu- 
lation.     The   involun- 
tary brushing  of  a  fly 
from  the  face   or  the 
attempt  to  move  away 
from  the  source  of  an- 
noyance w^hen  tickled 
with  a  feather,  are  other  examples.    In  a  reflex  act,  a  person  does 
not  think  before  acting.     The  nervous  impulse  comes  from  the 
outside  to  cells  that  are  not  in  the  cerebrum.     The  message  is 
short-circuited  back  to  the  surface  by  motor  nerves,  without  ever 
having  reached  the  thinking  centers.     The  nerve  cells  which  take 
charge  of  such  acts  are  located  in  the  cere]-)ellum  or  spinal  conl. 
But  some  reflex  acts  may  be  controlled  in  part  by  the  will.      Wo 
need  not,  for  instance,  brush  away  a  fly,  although  we  cannot  stop 
the  churning  of  the  stomach  or  the  process  of  breathing,  yet  sud- 
den fright  may  cause  us  to  take  a  certain  sharp  or  long  breath  or 


Regions  of  the  head  and  action  of  the  different  partx 
of  the  brain. 


408 


HUMAN   PHYSIOLOGY 


may  cause  nausea  or  even  vomiting.     The  glands  of  the  stomach 
will  not  secrete  unless  a  proper  stimulation  has  been  given  to 

them  by  food  entering  the  stomach. 
When  food  reaches  the  gland,  the 
message  is  sent  from  the  nerve  endings 
in  the  gland,  to  the  reflex  nervous 
center.  The  gland  begins  to  secrete 
its  fluid  on  the  receipt  of  a  return 
message  from  that  center.  Each  set 
of  glands  in  the  digestive  tract  acts  in 
a  similar  manner,  and  thus  digestive 
fluid  is  poured  out,  and  digestion  is 
accomplished. 

Automatic  Acts.  —  Some  acts,  how- 
ever, are  learned  by  conscious  thought, 
as  writing,  walking,  running,  or  swim- 
ming. Later  in  life,  however,  these 
activities  become  automatic.  The  ac- 
tual performance  of  the  action  is  then 
taken  up  by  the  cerebellum,  medulla, 
and  spinal  ganglia.  Thus  the  think- 
ing portion  of  the  brain  is  relieved  of 
part  of  its  work. 

Habit  Formation.  —  The  training  of 
the  different  areas  in  the  cerebrum  to 
do  their  work  well  is  the  object  of  edu- 
cation. When  we  learned  to  write, 
we  exerted  conscious  effort  in  order  to 
make  the  letters.  Now  the  act  of  forming  the  letters  is  done  with- 
out thought.  By  training,  the  act  has  become  automatic.  In 
the  beginning,  a  process  may  take  much  thought  and  many  trials 
before  we  are  able  to  complete  it.  After  a  little  practice,  the  same 
process  may  become  almost  automatic.  We  have  formed  a  habit. 
Habits  are  really  acquired  reflex  actions.  They  are  the  result  of 
nature's  method  of  training.  The  conscious  part  of  the  brain  has 
trained  the  cerebellum  or  spinal  cord  to  do  certain  things  that,  at 
first;  were  taken  charge  of  by  the  cerebrum. 


Diagram  of  the  path  of  a  nervous 
impulse  which  results  in  the  hand 
reaching  to  seize  an  object  seen 
with  the  eye;  C,  cerebrum;  Cb, 
cerebellum;  M,  medulla  oblon- 
gata ;  MC,  motor  center  in  brain  ; 
OC,  optic  center  in  brain;  P, 
pons  Varolii;  Q,  corpora  quadri- 
gemina;  S,  spinal  cord;  T,  optic 
thalami. 


THE  NERVOUS  SYSTEM 


409 


Importance  of  forming  Right  Habits.  Danger  of  Strong  Drink. 
—  Among  the  habits  early  to  be  acquired  are  tlie  habits  of  study- 
ing properly,  of  concentrating  the  mind,  of  learning  self-control, 
and  above  all,  the  habit  of  contentment.  Get  the  most  out  of 
the  world  about  you.  Remember  that  the  immediate  efToct  in 
the  study  of  some  subjects  in  school  may  not  l)e  great,  but  the 
cultivation  of  certain  methods  of  thinking  may  be  of  the  greatest 
importance  later  in  life. 

''  The  hell  to  be  endured  hereafter,  of  which  theology  tells,  is 
no  worse  than  the  hell  we  make  for  ourselves  in  this  world  by 
habitually  fashioning  our  characters  in  the  wrong  way.     Could  the 
young   but    realize 
how  soon  they  will 
become  mere  walk- 
ing bundles  of  hab- 
its, they  would  give 
more  heed  to  their 
conduct    while    in 
the    plastic     state. 
We  are  spinning  our 
own  fates,  good  or 
evil,    and  never  to 
be  undone.    Every 
smallest    stroke    of 
virtue  or  of  vice  leaves  its  never-so-little  scar.     The  drunken  Rip 
Van  Winkle,  in  Jefferson's  play,  excuses  himself  for  every  fresh 
dereliction  by  saying,  '  I  won't  count  this  time  !  '     Well !   he  may 
not  count  it,  and  a  kind  Heaven  may  not  count  it;   but  it  is  l)oing 
counted  none  the  less.    Down  among  his  nerve  cells  and  fibers  the 
molecules  are  counting  it,  registering  and  storing  it  up  to  ])e  used 
against  him  when  the  next  temptation  comes.     Notliing  we  ever 
do  is,  in  strict  scientific  literalness,  wiped  out.    Of  course  tliis  has 
its  good  side  as  well  as  its  bad  one.     As  we  become  permanent 
drunkards  by  so  many  separate  drinks,  so  we  become  saints  in 
the  moral,  and  authorities  in  the  practical  and  scientific,  spheres 
by  so  many  separate  acts  and  hours  of  work.     T.ot  no  youth  \\\\\o 
any  anxiety  about  the  upshot  of  his  education,  whatever  the  hno 


Diagram  of  the  path  of  a  simple  nervous  reflex  action. 


410  HUMAN   PHYSIOLOGY 

of  it  may  be.  If  he  keep  faithfully  busy  each  hour  of  the  work- 
ing day,  he  may  safely  leave  the  final  result  to  itself.  He  can  with 
perfect  certainty  count  on  waking  up  some  fine  morning,  to  find 
himself  one  of  the  competent  ones  of  his  generation,  in  whatever 
pursuit  he  may  have  singled  out."  —  James,  Psychology. 

Necessity  of  Food,  Fresh  Air,  and  Rest.  —  The  nerve  cells,  like  all 
other  cells  in  the  body,  are  continually  wasting  away  and  being 
rebuilt.  Oxidation  of  food  material  is  more  rapid  when  we  do 
mental  work.  The  cells  of  the  brain,  like  muscle  cells,  are  not 
only  capable  of  fatigue,  but  show  this  in  changes  of  form  and  of 
contents.  Food  brought  to  them  in  the  blood,  plenty  of  fresh 
air,  especially  when  engaged  in  active  brain  work,  and  rest  at 
proper  times,  are  essential  in  keeping  the  nervous  system  in  con- 
dition. One  of  the  best  methods  of  resting  the  brain  cells  is  a 
change  of  occupation.  Tennis,  golf,  baseball,  and  other  outdoor 
sports  combine  muscular  exercise  with  brain  activity  of  a  different 
sort  from  that  of  business  or  school  work. 

Necessity  of  Sleep.  —  Sleep  is  an  essential  factor  in  the  health  of 
the  brain,  especialh'  for  growing  children.  Most  brain  cells  attain 
their  growth  early  in  life.  Changes  occur,  however,  until  some 
time  after  the  school  age.  Ten  hours  of  sleep  should  be  allowed 
for  a  child,  and  at  least  eight  hours  for  an  adult.  At  this  time, 
only,  do  the  brain  cells  have  opportunity  to  rest  and  store  food  and 
energ}^  for  their  working  period. 

Effects  of  Alcohol.  — Alcohol  has  the  effect  of  temporarily  para- 
lyzing the  nerve  centers.  The  first  effect  is  that  of  exhilaration. 
This,  however,  is  a  false  feeling,  the  alcohol  having  paralyzed  the 
sense  of  fatigue.  A  man  may  do  more  work  for  a  time  under  the 
influence  of  this  false  feeling  of  exhilaration,  but  it  is  of  short 
duration  and  is  invariably  followed  by  a  period  of  depression  and 
inertia.  In  this  latter  state,  a  man  will  do  less  work  than  before. 
He  frequently  takes  more  alcohol  to  renew  the  feeling  of  buoyancy, 
and.  in  this  way  the  alcohol  habit  may  be  formed.  In  larger 
quantities,  alcohol  has  the  effect  of  completely  paralyzing  the 
nerve  centers.  This  is  seen  in  the  case  of  a  man  ''dead  drunk." 
He  falls  in  a  stupor  because  all  of  the  centers  governing  speech, 
sight,  locomotion,  etc.,  have  been  temporarily  paralyzed.     If  a 


THE  NERVOUS  8Y8TKM  41] 

man  takes  a  very  large  amount  of  alcohol,  even  the  nerve  centere 
governing  respiration  and  circulation  may  become  poisoned,  and 
the  victim  may  die. 

Influence  of  Alcohol  on  the  Nervous  System.  —  The  exact  action 
of  alcohol  upon  the  human  nervous  system  at  every  stage  of  the 
above-mentioned  process  has  not  as  yet  been  completely  accounted 
for. 

It  is  agreed  that  in  large  or  continued  amounts  alcohol  has  a 
narcotic  effect;  that  it  first  dulls  or  paralyzes  the  nerve  centers 
which  control  our  judgment,  and  later  acts  upon  the  so-called 
motor  centers,  those  which  control  our  muscular  activities. 

The  reason  then  that  a  man  in  the  first  stages  of  intoxication 
talks  rapidly  and  sometimes  wittily,  is  because  the  centers  of 
judgment  are  paralyzed.  This  frees  the  speech  centers  from  con- 
trol exercised  by  our  judgment  with  the  resultant  rapid  and  free 
flow  of  speech. 

In  small  amounts  alcohol  is  believed  by  some  physiologists  to 
have  always  this  same  narcotic  effect,  while  other  physiologists 
think  that  alcohol  does  stimulate  the  brain  centers,  especially  the 
higher  centers,  to  increased  activity.  Many  scientific  and  profes- 
sional men  use  alcohol  in  small  amounts  for  this  stimulation 
and  report  no  seeming  harm  from  the  indulgence.  Others,  and 
by  far  the  larger  number,  agree  that  this  stimulation  from  alcohol 
is  only  apparent  and  that  even  in  the  smallest  amounts  ak-oliol 
has  a  narcotic  effect.  One  of  the  most  serious  effects  of  alcohol 
is  the  lowered  resistance  of  the  body  to  disease.  It  has  been 
proved  that  a  much  larger  proportion  of  liard  drinkers  die  from 
infectious  or  contagious  diseases  than  from  special  diseased  con- 
ditions due  to  the  direct  action  of  alcohol  on  the  organs  of  the 
body.  This  lowered  resistance  is  shown  in  increased  liabiUty  to 
contract  disease  and  increased  severity  of  the  disease. 

But  many  cases  of  illness  are  directly  due  to  the  action  of 
alcohol  on  the  tissues.  ''Such  chronic  diseased  conditions 
arise  from  the  gradual  poisoning  of  the  system  by  the  con- 
tinued use  of  beverages  containing  alcohol.  Even  though 
we  admit  that  alcohol  in  a  definite  small  amount  is.  in  some 
cases  at  least,  fully  oxidized   Id    the   body,  Uke   other   cai'bo- 


412  HUMAN   PHYSIOLOGY 

hydrates,  and  so  supplies  energy  as  food,  we  must  never  forget 
that  different  constitutions  may  be  differently  affected,  and  condi- 
tions as  to  climate,  temperament,  and  habits  of  Ufe  may  cause 
variations  in  its  influence  upon  health  and  character.  We  can 
never  know  perfectly  the  nature  of  all  the  innumerable  strains 
of  hereditary  tendency  which  unite  to  make  an  individual  what 
he  is.  Some  one  of  these  may  have  impressed  upon  the  nerve 
cells  an  instability,  a  weakness,  a  peculiar  susceptibility  to  the 
influence  of  alcohol,  so  that  the  first  taste  may  arouse  the  insatiable 
craving  which  leads  to  dipsomania.  In  another  case,  the  inherited 
weakness  may  render  the  child  of  an  inebriate  an  epileptic,  an 
imbecile,  or  a  consumptive.  We  can  never  foresee  just  how  the 
transmitted  nervous  weakness  will  manifest  itself,  but  as  a  rule 
the  descendants  of  those  whose  systems  are  poisoned  by  alcohol 
are  enfeebled  in  body  or  mind  or  both. 

"  But  suppose  a  man  to  have  derived  from  his  ancestors  a 
sound  constitution  and  to  have  become  addicted  to  the  moderate 
use  of  alcohol;  the  insidious  nature  of  the  dangerous  substance 
may  gradually  lead  him  to  consume,  insensibly  perhaps,  only  a  little 
more  than  the  cells  can  oxidize.  Without  realizing  it,  he  may 
slowly  poison  his  system.  The  primary  effect  is  upon  the  brain; 
there  is  congestion  and  overexcitement  of  the  nerve  cells  there  — 
conditions  which  gradually  extend  to  the  nerve  cells  of  the  spinal 
cord;  inflammation  sets  in,  and  there  follows  fibrous  degeneration 
of  the  tissues,  substituting  an  inferior  form  for  the  specialized 
tissues  which  do  the  work  of  the  organs  in  various  parts  of  the 
body.  Paralysis  may  result,  or  epilepsy,  or  dyspepsia  from  lack 
of  the  due  amount  of  nervous  influence  upon  the  digestive  organs, 
or  any  one  of  a  thousand  forms  of  disorder,  some  of  which  have 
been  mentioned  in  preceding  chapters.  Though  a  man  may  never 
drink  to  intoxication,  and  never  realize  that  he  is  using  alcohol  to 
excess,  he  may  nevertheless  become  seriously  diseased  in  conse- 
quence of  his  moderate  indulgence,  or  what  he  believes  to  be  such, 
while  wondering  why  he  is  not  well  and  strong.  Still  less  does 
he  consider  the  legacy  of  evil  which  he  may  be  laying  up  for  his 
children. 

"  Life  insurance  companies  have  gathered  an  immense  body 


THE   NERVOUS   SYSTEM  4U 

of  statistics  respecting  human  life,  with  sole  reference  to  their 
bearing  upon  the  business  of  insurance,  and  it  is  well  known  that 
life  insurance  companies  regard  policies  upon  the  lives  of  drinkinp- 
men  —  even  '  moderate  drinkers  '  —  as  involving  '  extra  risk.' 
Their  figures  have  convinced  them  that  the  man  who  uses  no  alco- 
holic beverages  is  likely  to  live  longer  than  one  who  does."  — 
Macy,  Physiology. 

"  Alcohol  a  Cause  of  Mental  Disorders.  —  If  you  look  round  and 
try  to  find  out  the  primary  causes  of  disease  and  poverty  and  crinie 
and  misery,  you  are  over  and  over  again  thrown  back  on  the  use  of 
alcohol.  One  cannot  read  the  newspapers  and  reports  of  judges 
without  seeing  that  alcohol  accounts  for  a  very  large  proportion 
of  what  is  evil  in  our  daily  life.  It  is  sapping  the  foundation  of 
our  national  life,  and  if  we  could  do  away  with  all  the  disease  and 
poverty  and  crime  caused  by  alcohol,  the  questions  which  confront 
us  would  be  solved  very  easily. 

"  The  Influence  of  Alcohol  upon  the  Morals.  —  The  most  highly 
specialized  characteristics  are  fir=5t  impaired,  and  thus  the  spiritual 
faculty,  if  I  may  so  term  it,  first  becomes  blunted  by  the  use  of 
alcohol.  Following  this  in  rapid  succession  there  is  blunting  of 
the  moral  sense;  a  slight,  though  distinctly  perceptible,  inter- 
ference with  the  intellectual  faculties,  which  leads  to  what  we 
might  call  blurring  of  the  reasoning  power;  then  follows  a  distinct 
diminution  in  the  power  of  rapidity  and  accuracy  of  perception. 
At  none  of  these  stages  would  a  man  admit  that  he  was  under 
the  influence  of  alcohol;  but  these  powers  are  just  as  assuredly 
under  its  influence  as  are  the  muscles  which  can  no  longer  act 
coordinately  to  enable  a  man  to  walk  straight."  —  Professor  (i. 
Sims  Woodhead. 

The  Influence  of  Alcohol.  — ''Alcohol  acts  primarily  on  the 
nerve  cells,  changing  their  granular  matter,  breaking  up  their 
nutrition,  and  changing  their  dynamic  force.  This  action  is 
followed  by  contraction  of  the  dendrites,  swelling  and  atrophy  of 
these  fibers,  also  shrinking  of  cell  walls,  as  in  fatigue,  and  coalescing 
and  disappearance  of  the  granular  matter  of  proto}^lasin."  — 
Journal  of  the  American  Medical  Association,  November,  1S9S. 

''Alcohol  does  not  affect  all  the  spinal  cells  equally,  and  in  the 


414  HUMAN  PHYSIOLOGY 

early  stages  the  changes  are  rather  indefinite,  a  greater  sharpness 
of  contour  being  the  most  obvious.  In  the  cerebrum  the  cells 
appear  as  mere  shadows,  both  substances  disappearing,  whilst 
the  nuclei  are  also  altered."  —  London  Lancet,  October  31,  1896, 
p.  1245. 

"  Just  why  the  alcohol  should  select  a  set  of  nerves  on  which  to 
act  at  one  time  and  a  different  set  at  another  does  not  at  once 
appear,  but  it  is  a  well-authenticated  fact  that  it  has  a  selective 
power.  Most  hkely  the  explanation  lies  in  the  chemical  or  elec- 
trical condition  of  the  white  substance  at  the  time  of  action,  or 
it  may  be  attributable  to  the  different  chemical  constituents  of 
the  liquor  used."  —  Dr.  Wilkins,  in  the  New  York  Medical  Jour- 
nal, September  22,  1894. 

"Professor  Kraepelin  of  Heidelberg  tried  a  number  of  experi- 
ments on  individuals,  with  the  object  of  seeing  whether  a  small 
quantity  of  alcohol  hindered  the  nervous  transmission  of  intel- 
ligence to  the  brain.  Flags  were  raised  at  a  given  distance, 
and  the  exact  time  was  noted  when  the  various  men  experimented 
upon  observed  the  raising  of  the  flag.  The  result  proved  that  the 
watchers  who  had  been  given  a  small  quantity  of  alcohol,  though 
they  felt  that  they  had  seen  the  flag  rise  sooner  than  those  who 
had  received  no  alcohol,  actually  took  longer."  —  Hall,  Elementary 
Physiology. 

Professor  Woodhead  says,  ''After  careful  examination  of  the 
whole  question,  physiologists  —  and  among  physiologists  I  include 
those  who  maintain  alcohol  may  be  useful,  as  well  as  those  who 
hold  that  it  is  harmful  —  have  come  to  the  conclusion  that  the 
principal  action  of  alcohol  is  to  blunt  sensation,  and  to  remove 
what  we  may  call  the  power  of  inhibition  by  blunting  the  higher 
centers  of  the  brain." 

Professor  David  Starr  Jordan  in  the  Popular  Science  Monthly, 
February,  1898,  said:  ''  The  healthy  mind  stands  in  clear  and 
normal  relations  with  Nature.  It  feels  pain  as  pain.  It  feels 
action  as  pleasure.  The  drug  which  conceals  pain  or  gives  false 
pleasure  when  pleasure  does  not  exist  forces  a  lie  upon  the  nervous 
system.  The  drug  which  disposes  to  reverie  rather  than  to  work, 
which  makes  us  feel  well  when  we  are  not  v/ell,  destroys  the  sanity 


THE  NERVOUS  SYSTEM  41  o 

of  life.  All  stimulants,  narcotics,  tonics,  which  affect  the  nen-ous 
system  in  whatever  way,  reduce  the  truthfuhiess  of  seiisation, 
thought,  and  action.  Toward  insanity  all  such  influences  lead; 
and  their  effect,  slight  though  it  be,  is  of  the  same  nature  as  mania. 
The  man  who  would  see  clearly,  think  truthfully,  and  act  effectively 
must  avoid  them  all.  Emergency  aside,  he  cannot  safely  force 
upon  his  nervous  system  even  the  smallest  falsehood." 

Dr.  Hammond  said:  ''The  more  purely  intellectual  qualities 
of  the  mind  rarely  escape  being  involved  in  the  general  disturbance 
[caused  by  alcohol].  The  power  of  application,  of  appreciating 
the  bearing  of  facts,  of  drawing  distinctions,  of  exercising  the 
judgment  aright,  and  even  of  comprehension,  are  all  more  or  less 
impaired.  The  memory  is  among  the  first  faculties  to  suffer.  ,  . 
The  will  is  always  lessened  in  force  and  activity.  The  ability 
to  determine  between  two  or  more  alternatives,  to  resolve  to  act 
when  action  is  necessary,  no  longer  exists  in  full  power,  and  the 
individual  becomes  vacillating,  uncertain,  the  prey  to  his  various 
passions,  and  to  the  influence  of  vicious  counsels.'' 

"Helmholtz  told  us  in  his  autobiography  that  if  he  took  wine 
while  occupied  with  a  mathematical  or  scientific  problem,  his 
thinking  powers  were  interfered  with,  and  he  had  to  wait  for  the 
alcoholic  effects  to  work  off  before  his  inspiration  returned."  — 
Dr.  Adolph  Rupp,  Neiu  York  Medical  Journal,  July  9,  1898. 

"Finally  we  have  still  to  declare  that  alcohol  hinders  the  action 
of  the  highest  mental  faculties.  A  remark  made  by  Helniholtz 
at  the  celebration  of  his  seventieth  birthday  is  very  interesting 
in  this  connection.  He  spoke  of  the  ideas  flashing  up  from  the 
depths  of  the  unknown  soul,  that  lies  at  the  foundation  of  every 
truly  creative  intellectual  production,  and  closed  his  account  of 
their  origin  with  these  words:  'The  smallest  quantity  of  an  alco- 
hoUc  beverage  seemed  to  frighten  these  ideas  away.'  "  — Dh.  G. 
Sims  Woodhead,  Professor  of  Pathology,  Cambridge  University. 

England. 

W.  Boyd  Dawkins  says:  "I  cannot  drink  beer  when  I  am  using 
my  brain,  and  do  not  take  it  when  I  have  anything  to  think  al)out." 
—  Quoted  by  Dr.  M.  L.  Holbrook,  Journal  Medical  Temperance 
Association f  January,  1898,  p.  21. 


416  HUMAN   PHYSIOLOGY 

"  Some  people  imagine  that  after  the  use  of  alcohol  they  can  do 
things  more  quickly,  that  they  are  brisker  and  sharper,  but  exact 
measurement  shows  that  they  are  slower  and  less  accurate.  Men 
believe  that  they  are  wiser  and  brighter,  but  their  sayings  are  more 
automatic  and  apt  to  be  profane.  To  quote  Dr.  Lauder  Brunton, 
of  Oxford  University,  England,  ^  It  produces  progressive  paralysis 
of  the  judgment,'  and  this  begins  with  the  first  glass.  Men  say 
and  do,  even  after  a  single  glass  of  drink,  what  they  would  not  say 
or  do  without  it,  and  therefore  it  clearly  affects  the  brain  and 
diminishes  self-control."  —  Adolph  Fick,  Professor  of  Physiology, 
Wiirzburg,  Germany. 

Professor  von  Bunge  {Text-hook  of  Physiological  and  Patholog- 
ical Chemistry)  of  Switzerland,  says  that:  ''The  stimulating 
action  which  alcohol  appears  to  exert  on  the  brain  functions  is 
only  a  paralytic  action.  The  cerebral  functions  which  are  first 
interfered  with  are  the  power  of  clear  judgment  and  reason.  No  man 
ever  became  witty  by  aid  of  spirituous  drinks.  The  lively  ges- 
ticulations and  useless  exertions  of  intoxicated  people  are  due  to 
paralysis,  —  the  restraining  influences,  which  prevent  a  sober  man 
from  uselessly  expending  his  strength,  being  removed." 

*'  The  capital  argument  against  alcohol,  that  which  must  even- 
tually condemn  its  use,  is  this,  that  it  takes  away  all  the  reserved 
control,  the  power  of  mastership,  and  therefore  offends  against  the 
splendid  pride  in  himself  or  herself,  which  is  fundamental  in  every 
man  or  woman  worth  anything."  —  Dr.  John  Johnson,  quoting 
Walt  Whitman. 

The  Drink  Habit.  —  The  harmful  effects  of  alcohol  (aside  from 
the  purely  physiological  effect  upon  the  tissues  and  organs  of  the 
body)  are  most  terribly  seen  in  the  formation  of  the  alcohol  habit. 
The  first  effect  of  drinking  alcoholic  liquors  is  that  of  exhilaration. 
After  the  feeling  of  exhilaration  is  gone,  for  this  is  a  temporary 
state,  the  subject  feels  depressed  and  less  able  to  work  than  before 
he  took  the  drink.  To  overcome  this  feeling,  he  takes  another 
drink.  The  result  is  that  before  long  he  finds  a  habit  formed  from 
which  he  cannot  escape.  With  body  and  mind  weakened,  he 
attempts  to  break  off  the  habit.  But  his  will,  too,  has  suffered 
from  over  indulgence.    He  has  become  a  victim  of  the  drink  habit  1 


THE   NERVOUS  SYSTEM  117 

Self-indulgence,  be  it  in  gratification  of  such  a  simple  desire  as 
that  for  candy  or  the  more  harmful  indulgence  in  tohacco  or  al- 
coholic beverages  is  dangerous  —  not  only  in  its  immediate  efTects 
on  the  tissues  and  organs,  but  in  its  more  far-reaching  efTects  on 
habit  formation. 

The  Moral,  Social,  and  Economic  Effect  of  Alcoholic  Poisoning.— 
In  the  struggle  for  existence,  it  is  evident  that  the  man  whose  in- 
tellect is  the  quickest  and  keenest,  whose  judgment  is  most  sound, 
is  the  man  who  is  most  likely  to  succeed.  The  paralyzing  effect 
of  alcohol  upon  the  nerve  centers  must  place  the  drinker  at  a  dis- 
advantage. In  a  hundred  ways,  the  drinker  sooner  or  later  feels 
the  handicap  that  the  habit  of  drink  has  imposed  upon  him. 
Many  corporations,  notably  several  of  our  greatest  railroads  (the 
New  York  Central  Railroad  among  them),  refuse  to  employ  any 
but  abstainers  in  positions  of  trust.  Few  persons  know  the  num- 
ber of  railway  accidents  due  to  the  uncertain  eye  of  some  engineer 
who  mistook  his  signal,  or  the  hazy  inactivity  of  the  ])rain  of  some 
train  dispatcher  who,  because  of  drink,  forgot  to  send  the  tele- 
gram that  was  to  hold  the  train  from  wreck. 

In  business  and  in  the  professions,  the  story  is  the  same.  The 
abstainer  wins  out  over  the  drinking  man. 

Not  alone  in  activities  of  life,  hut  in  the  length  of  life  has  the  ab- 
stainer the  advantage.  Figures  presented  by  life  insurance  com- 
panies show  that  the  nondrinkers  have  a  considerably  greater 
chance  of  long  life  than  do  drinking  men.  So  decided  are  these 
figures  that  several  companies  have  lower  premiums  for  the  non- 
drinkers  than  for  the  drinkers  who  insure  with  them. 

"  Other  Narcotics  in  Common  Use.  —  Narcotics  are  very  widely 
used  by  the  human  family  for  the  relief  which  they  give  from  j)ain 
or  fatigue,  or  for  the  direct  pleasurable  sensations  which  they 
impart.  All  are  deadly  poisons  w^hen  taken  in  sufficient  quan- 
tities.    Those  most  common  (after  alcohol)  are  tobacco  and  opium. 

"  It  has  already  been  shown  that  tobacco  may  affect  unfavorably 
many  parts  of  the  system,  and  is  especially  injurious  to  the  young. 
It  stimulates  in  small  quantities  and  narcotizes  in  larger  ones, 
working  its  efTects  directly  upon  the  nervous  system.  Nicotine 
is  a  powerful  poison  found  in  tobacco.     It  affects  the  ner\'e  cells, 

hunter's  BIOL. — 27 


418  HUMAN   PHYSIOLOGY 

injures  the  brain,  and  leads  especially  to  weakness  of  the  heart  by 
interfering  with  its  supply  of  nervous  force.  Many  cases  of  cancer 
of  mouth  and  throat  are  believed  to  have  resulted  from  tobacco 
smoking. 

"  Opium,  for  its  benumbing  influence  upon  the  nerves,  is  used  by 
large  numbers  of  persons,  especially  in  Oriental  lands.  Its  con- 
tinued use  deranges  all  the  digestive  processes,  disorders  the  brain, 
and  weakens  and  degrades  the  character.  Like  alcohol,  it  pro- 
duces an  intolerable  craving  for  itself,  and  the  strongest  minds 
are  not  proof  against  the  deadly  appetite. 

"  Self-control  versus  Appetite.  —  Man  is  a  bundle  of  appetites. 
Every  organ,  every  cell  even,  craves  its  appropriate  stimulus.  Ani- 
mals under  natural  conditions  gratify  the  appetites  as  they  arise 
only  to  that  extent  which  is  healthful  for  the  whole  body.  Man 
alone,  whose  highly  developed  brain  is  overlord  to  the  rest  of  his  sys- 
tem, permits  an  unwholesome  indulgence  of  appetite  to  interfere 
with  this  general  well-being.  Alcohol,  opium,  and  their  like  are  far 
from  being  the  only  substances  whose  excessive  use  injures  the 
organism  and  degrades  character.  Children  are  often  allowed 
to  indulge  a  natural  fondness  for  sweets  to  an  extent  which  is 
ruinous  to  digestion;  for  sugar,  which  is  a  useful  and  necessary 
food  in  suitable  quantities,  in  larger  ones  acts  injuriously  upon  the 
system.  Boys  pampered  with  dainties  from  infancy  logically  infer 
that  a  fancy  for  cigars  or  beer  may  be  similarly  gratified.  Appe- 
tite for  even  the  most  wholesome  food  may  be  in  excess  of  bodily 
needs,  and  the  practice  of  gluttony  is  certain  to  derange  nutrition. 

"  A  child  should  be  early  taught  that  because  he  '  likes  '  a 
certain  article  of  food  he  should  not  therefore  continue  to  eat  it 
after  natural  hunger  is  satisfied,  or  at  times  when  he  does  not  need 
food;  while  to  persist. in  eating  or  drinking  that  which  experience, 
or  the  advice  of  those  competent  to  judge,  has  taught  him  to  be 
harmful,  should  be  regarded  as  unworthy  a  rational  being. 

"  These  are  but  illustrations  of  the  manifold  forms  of  intemper- 
ance which  work  untold  harm  to  the  physical  and  moral  natures. 
There  seems  no  possibility  of  improvement  to  our  race  except 
as  the  young  are  led  to  recognize  the  manliness  and  dignity  of 
controUing  one's  appetites."  —  Macy,  Physiology, 


XXXVI.     THE   SENSES 


itk 


Nerves  in  the  skin;  a,  nerve  fiht-r ;  b.  tactile 
papillae,  containing  a  tactile  corpuscle  ;  e, 
papillae  containing  blood  vessels.  (After 
Benda.) 


Touch.  —  In  animals  having  a  hard  outside  coverinpr,  such  as 
certain  worms,  insects,  and  crustaceans,  minute  hairs,  which  are 
sensitive  to  touch,  are  found  growing  out  from  the  body  covering. 
At  the  base  of  these  hairs  are 
found  nerve  cells  which  send 
a  nerve  fiber  inward  to  the 
central  nervous  system. 

Organs  of  Touch.  —  In  man, 
the  nervous  mechanism  which 
governs  touch,  is  located  in 
the  folds  of  the  dermis  or  in 
the  skin.  Special  nerve  end- 
ings, called  the  tactile  corpus- 
cles, are  there  found.  They 
are  inclosed  in  a  sheath,  or 
capsule,  of  connective  tissue. 
Inside  is  a  complicated  nerve  ending,  and  ner\^e  fibers  are  sent  in- 
ward to  the  central  nervous  system.  The  number  of  tactile  cor- 
puscles present  in  a  given  area  of  the  skin  determines  the  accuracy 
and  ease  with  which  objects  may  be  known  by  touch. 

If  you  test  the  different  parts  of  the  body,  as  the  back  of  the  liand.  tho 
neck,  the  skin  of  the  arm,  of  the  back,  or  the  tip  of  the  tonf^uc,  witli  a  i)air 
of  open  dividers,  a  vast  difference  in  the  accuracy  with  which  tho  two  p(»ints 
may  be  distinguished  is  noticed.  On  the  tip  of  the  tongue,  tlio  two  points 
need  only  be  separated  by  2V  of  an  inch  to  be  so  distiiiKui.^hod.  In  the 
small  of  the  back,  a  distance  of  two  inches  may  be  reached  before  the 
dividers  feel  like  two  points. 

Temperature,  Pressure,  Pain.  —  The  feeling  of  temperature, 
pressure,  and  pain,  the  latter  only  in  part,  are  determined  by  organs 
in  the  skin.  Physiologists  believe,  however,  that  these  organs  are 
distinct  from  the  apparatus  which  distinguishes  touch. 

Taste  Organs.  — The  surface  of  the  tongue  is  folded  into  a  num- 
ber of  little  projections  known  as  papilhe.     These  may  be  more 

419 


420 


HUMAN   PHYSIOLOGY 


Taste  Cells 

^Supporting 
Cells 


A,  isolated  taste  bud,  from 
whose  upper  free  end 
project  the  ends  of  the 
taste  cells;  S,  supporting 
or  protecting  cell;  C, 
sensory  cell. 


-Wall 


easily  found  on  your  own  tongue  if  a  drop  of  vinegar  is  placed  on 
its  broad  surface.     In  the  folds,  between  these  projections  on  the 

top  and  back  part  of  the  tongue,  are  lo- 
cated the  organs  of  taste.  These  organs  are 
called  taste  buds. 

Each  taste  bud  consists  of  a  collection  of  spindle- 
shaped  nerve  cells,  each  cell  tipped  at  its  outer 
en'd  with  a  hairlike  projection.  These  cells  send 
inward  fibers  which  ultimately  reach  the  brain. 
The  sensory  cells  are  surrounded  by  a  number  of 
protecting  cells  which  are  arranged  in  layers  about 
them.  Thus  the  organ  in  longitudinal  section 
looks  somewhat  like  an  onion  cut  lengthwise. 

How  we  Taste.  — Four  kinds  of  substances 
may  be  distinguished  by  the  sense  of  taste. 
These  are  sweet,  sour,  bitter,  and  salt.  Certain  taste  cells  lo- 
cated near  the  back  of  the  tongue  are  stimulated  only  by  a  bitter 
taste.  Sweet  substances  are  per- 
ceived by  cells  near  the  tip  of  the 
tongue.  A  substance  must  be 
dissolved  in  fluid  in  order  to  be 
tasted.  Many  things  which  we 
believe  we  taste,  are  in  reality 
perceived  by  the  sense  of  smell. 
Such  are  spicy  sauces  and  flavors 
of  meats  and  vegetables.  This 
may  easily  be  proved  by  holding  the  nose  and  chewing,  with  closed 
eyes,  several  different  substances,  such  as  an  apple,  an  onion,  and 
a  raw  potato. 

Smell.  —  The  sense  of  smell  is  located  in  the  membrane  lining 
the  upper  part  of  the  nose.  Here  are  found  a  large  number  of 
rod-shaped  cells  which  are  connected  with  the  forebrain  by  means 
of  the  olfactory  nerv^e.  In  order  to  perceive  odors,  it  is  necessary 
to  have  them  diffused  in  the  air;  hence  we  sniff  or  draw  in  more 
air  over  the  olfactory  cells  so  as  to  bring  more  odoriferous  particles 
to  them  and  thus  to  distinguish  the  odor. 

''  Effects  of  Alcohol  upon  Taste  and  Smell.  —  The  habitual  use 
of  drinks  containing  alcohol,  of  tobacco,  and  of  very  strongly 


Taste  Buds^: 


Nerves 


Section  of  cir  cum  vallate  papilla. 


THE  SENSES  4JJ 

flavored  foods  is  found  to  dull  the  sense  of  t;iste.  and  ],v  al(.<,],.,l  .,t 
least,  the  olfactories  are  rendered  less  acute."  —  Macv",  / V///.svWoV//. 

The  Organ  of  Hearing. -The  organ  of  hearing  is  the  ear.     In  a  fi.h 
irog,  or  reptile,  the  outer  ear,  so  prominent  in  man,  is  entirely  lacking     Tl..^ 
outer  ear  consists  of  a  funnel-like  organ  composed  largely  „f  cartilage  whirli 
IS  of  use  in  collecting  sound  waves.     This  part  of  the  ear  ind.xes  the  audi- 
tory  canal  which  is  closed  at  the  inner  end  by  a  tightly  stretched  membrane 
the  tympanic  membrane.     We  have  seen  the  tympanic  membrane  of   the 
frog  on  the  outer  sur- 
face of  the  head.    The 
function  of  the  tym- 
panic membrane  is  to 
receive   sound  waves, 
for  all  sound  is  caused 
by  vibrations  in   the 
air,    these    vibrations 
being  transmitted,  by 
the  means  of  a  com- 
plicated apparatus 
found   in   the   middle 
ear,  to  the  real  organ 
of  hearing  located  in 
the  inner  ear. 

Middle  Ear. —  The 
middle  ear  in  man  is 
a  cavity  inclosed  by 
the  temporal  bone, 
and    separated    from 


Section  of  ear,  showing  auditory  canal,  middle  ear,  internal 
ear,  and  Eustachian  tube. 


the  outer  ear  by  the  tympanic  membrane.  A  little  tube  called  the  Eusta- 
chian tube  connects  the  inner  ear  with  the  mouth  cavity.  By  allowing  air  to 
enter  from  the  mouth,  the  air  pressure  is  equalized  on  the  ear  drum.  For 
this  reason,  we  open  the  mouth  at  the  time  of  a  heavy  concussion  and  thus 
prevent  the  rupture  of  the  delicate  tympanic  membrane.  Placed  directly 
against  the  tympanic  membrane  and  connecting  it  with  another  mem- 
brane, separating  the  middle  from  the  inner  ear,  is  a  chain  of  three  tiny 
bones,  the  smallest  bones  of  the  body.  The  outermost  is  called  the  /jam- 
mer; the  next  the  incus  or  anvil;  the  third  the  stirrup.  All  three  bones 
are  so  called  from  their  resemblances  in  shape  to  the  articles  for  which 
they  are  named.  These  bones  are  held  in  place  by  very  small  nujsch-s 
which  are  delicately  adjusted  so  as  to  tighten  or  relax  the  membranes  guard- 
ing the  middle  and  inner  ear. 

The  Inner  Ear.  —  The  inner  ear  is  one  of  the  most  complicated,  as  well 
as  one  of  the  most  delicate,  organs  of  the  body.     Deep  within  the  t<'m- 


422  HUMAN   PHYSIOLOGY 

poral  bone  there  are  found  two  parts,  one  of  which  is  called,  collectively, 
the  semicircular  canal  region,  the  other  the  cochlea  or  organ  of  hearing. 
Both  of  these  organs  consist  of  membranous  bags  lying  in  a  fluid  which 
partially  fills  the  bony  cavity  which  incloses  them.  These  membranous 
structures  themselves  also  contain  a  fluid.  The  semicircular  canals  are 
connected  with  the  cochlea  on  one  side,  and  are  separated  from  the  middle 
ear  only  by  a  membrane  and  the  fluid  which  surrounds  them.  There  are 
three  semicircular  canals,  delicate  membranous  bags  lying  in  a  watery 
fluid  and  surrounded  by  bone. 

It  has  been  discovered  by  experimenting  with  fish  in  which  the  semi- 
circular canal  region  forms  the  chief  part  of  the  ear,  that  it  has  to  do  with 
the  equilibrium  or  balancing  of  the  body.  We  gain  our  knowledge  of  our 
position  and  movements  in  space  by  means  of  the  semicircular  canals. 

That  part  of  the  ear  which  receives  sound  waves  is  known  as  the  cochlea, 
or  snail  shell,  because  of  its  shape.  This  very  complicated  organ  is  lined  with 
sensory  cells  provided  with  cilia.  The  cavity  of  the  cochlea  is  filled  with  a 
fluid ;  this  fluid  presses  against  the  membrane  and  separates  the  inner  from 
the  middle  car.  It  is  believed  that  somewhat  as  a  stone  thrown  into  water 
causes  ripples  to  emanate  from  the  spot  where  it  strikes,  so  sound  waves, 
transmitted  by  the  bones  of  the  middle  ear  to  the  membrane  guarding  the 
entrance  to  the  inner  ear,  are  transmitted  by  means  of  the  fluid  filling  the 
cavity  to  the  sensory  cells  of  the  cochlea  (collectively  known  as  the  organ 
of  Corti)  and  thence  to  the  brain  by  means  of  the  auditory  nerve. 

The  Character  of  Sound. — When  vibrations  which  are  received  by  the 
ear  follow  each  other  at  regular  intervals,  the  sound  is  said  to  be  musical. 
If  the  vibrations  come  irregularly,  we  call  the  sound  a  noise.  If  the  vibra- 
tions come  slowly,  the  pitch  of  the  sound  is  low;  if  they  come  rapidly,  the 
pitch  is  high.  The  ear  is  able  to  perceive  as  low  as  thirty  vibrations  per 
second  and  as  high  as  almost  thirty  thousand.  The  ear  can  be  trained  to 
recognize  sounds  which  are  unnoticed  in  untrained  ears. 

Care  of  the  Ear.  —  Some  of  the  cells  lining  the  cavity  of  the  outer  ear 
secrete  a  bitter  substance  called  wax.  This  wax,  which  aids  in  keeping  the 
canal  of  the  outer  ear  moist,  also  aids  in  keeping  foreign  matters,  especially 
living  insects,  out  of  the  ear.  In  removing  wax  or  dirt  no  sharp  pointed 
instrument  should  be  used.  Inflammation  of  the  ear  should  be  treated  by 
a  doctor,  as  at  such  times  pus  may  gather  in  the  inner  ear  in  sufficient 
quantity  to  rupture  the  tympanic  membrane.  In  serious  cases,  the  bone 
around  the  inner  ear  may  become  diseased  and  the  brain  affected.  The 
ear  should  be  protected  against  sudden  loud  sounds,  such  sounds  tending 
to  break  the  tympanic  membrane.  When  the  ear  is  sensitive  to  cold  or 
dampness,  a  small  wad  of  cotton  may  be  inserted  when  going  out  of  doors. 
This  should  always  be  removed  upon  entering  the  house. 

The  Eye. — The  eye  or  organ  of  vision  is  an  almost  spherical  body  which 
fits  into  a  socket  of  bone,  the  orhib.     What  might  be  the  function  of  this 


THE  SENSES 


423 


bony  socket?  A  stalklike  structure,  the  optic  nerve,  connects  the  eye  with 
the  bram.  Free  movement  is  obtained  by  means  of  six  little  muscles  which 
are  attached  to  the  outer  coat,  the  eyeball  and  to  the  bony  S(.cket  around 
the  eye.i  Notice  the  living  frog.  Compare  the  movements  of  your  own 
eye  with  those  of  the  frog.  Note  any  differences  in  position  of  the  eye  of 
the  frog  and  of  that  of  man,  and  try  to  account  for  these  difTercu.  Ixiok 

for  adaptations  for  the  protection  of  your  eye.  Among  such  adaptaticina 
are  the  position,  structure  of  the  lids,  and  the  lashes.     The  latter  are  useful 


in  protecting  the  eye  from  foreign  substances 
outer  lids  are  not  always  found  in 
lower  vertebrate  animals.  In  some 
vertebrates,  however,  as  in  the  bird, 
lizard,  frog,  and  some  lower  mam- 
mals, we  find  a  third  or  winking  eye- 
lid. In  man  this  eyelid  is  reduced  to 
a  small  fleshy  fold  seen  in  the  inner 
angle  of  the  eye.  Glands  which  se- 
crete a  salty,  watery  fluid  are  present. 
This  fluid  keeps  the  eye  moist,  and 
prevents  friction  between  the  eyeball 
and  its  coverings.  A  small  duct,  which 
can  be  found  in  the  inner  corner  of 
the  eye,  carries  off  all  waste  secretion 
into  the  nose.  During  a  cold,  when 
this  passage  is  stopped  up,  the  tears 
overflow.  Other  glands  which  secrete 
an  oil  prevent  tears,  under  normal 
circumstances,  from  flowing  out  of 
the  eyes. 


As  we  have  soon,  tlio  two 


o  /  l 

0J  (_  ^*- 


Section  of  the  retina;  .1,  rHafrr.im  of  the 
structure  of  the  retina  as  .s<'t'n  with  the 
compound  microscope;  B,  the  oji.M*ntial 
nervous  elements  of  tlie  ret  ina  as  <leinon- 
strated  by  the  Golgi  method  ;  /,  internal 
limiting  membrane;  2,  nerve-fiber  layw; 

3,  nerve-ceil     or     HJinclion-crli     layer; 

4,  inner  molecular  layer;  o,  iriner  granu- 
lar layer;  6,  outer  molecular  layer; 
7,  outer  jjranular  layer:  .•?.•'  '  '  ■'• 
iting  memlirane;  .'^i  nxl-anu  ; 
lU,  pigment-cell  layer. 


Internal  Structure.^  —  The  hu- 
man eyeball,  if  cut  in  a  longi- 
tudinal median  section,  from  the 
front  backwards,  will  show  the 
following  structures:  — 

The  wall  of  the  eveball  is  made  u]:>  of  three  coats.  An  outer 
tough  white  coat,  of  connective  tissue,  is  called  the  sclerotic  coat: 
this  coat  is  lacking  in  the  exposed  part  of  the  eyeball.  ])Ut  may  he 
seen  by  lifting  the  eyelid.  Under  the  sclerotic  coat,  in  front,  the 
eye  bulges  outward  a  little.     Here  the  outer  coat  is  rrplace<i  by 

1  Use  for  the  following  work  a  living  frog  

2  For  laboratory  work  on  the  eye  of  the  sheep  or  the  Imnuin  eye.  sec  Hunter  nntl 
Valentine,  Maniuil,  pages  189-192. 


424 


HUMAN   PHYSIOLOGY 


a  transparent  tough  layer  called  the  cornea.  A  second  cop.t,  the 
choroid,  is  supplied  with  blood  vessels  and  cells  which  bear  pigments. 
It  is  this  coat  which  we  see  through  the  cornea  as  the  colored  part 
of  the  eye  (the  iris).  In  the  center  of  the  iris  is  a  small  circular 
hole  (the  pupil).  The  iris  is  under  the  control  of  muscles,  and  may 
be  adjusted  to  varying  amounts  of  light,  the  hole  becoming  larger 
in  dim  light,  and  smaller  in  bright  light.     Watch  the  pupil  of 

a  cat's  eye,  in 
changing  the  ani- 
mal from  a  dark 
to  a  light  room. 
The  inmost  layer 
of  the  eye  is  called 
the  retina.  This 
is,  perhaps,  the 
most  delicate  layer 
in  the  entire  body. 
Despite  the  fact 
that  the  retina  is 
less  than  -g^^-  of 
an  inch  in  thick- 
ness, there  are  no 
less  than  eight 
layers  of  cells  in 
its  composition. 
The    optic    nerve 


Longitudinal  section  through  the  eye;  Sc,  sclerotic  coat ;  Ch,  cho- 
roid; O,  optic  nerve  ;  C,  cornea;  /.iris;  B,  blind  spot;  con,  con- 
junctiva; R,  retina;  Y,  yellow  spot;  L,  lens;  A,  anterior 
chamber,  filled  with  aqueous  humor;  V,  posterior  chamber, 
filled  with  vitreous  humor. 


enters  the  eye  from  behind  and  spreads  out  over  the  surface  of 
the  retina.  Its  finest  fibers  end  in  elongated  rodlike  and  cone- 
like cells.  The  retina  is  dark  purple  in  color,  this  color  being 
caused  by  a  layer  of  cells  next  to  the  choroid  coat.  This  accounts 
for  the  black  appearance  of  the  pupil  of  the  eye,  when  we  look 
through  the  pupil  into  the  darkened  space  within  the  eyeball. 
The  retina  acts  as  the  sensitized  plate  in  the  camera,  for  on  it  are 
received  the  impressions  which  are  transformed  and  sent  to  the 
brain  as  sensations  of  sight.  The  eye,  like  the  camera,  has  a  lens. 
This  lens  is  formed  of  transparent,  elastic  material.  It  is  found 
directly  behind  the  iris  and  is  attached  to  the  choroid  coat  by 


THE  SENSES 


4  25 


means  of  delicate  ligaments.  In  front  of  the  lens  is  a  small  cavity 
filled  with  a  watery  fluid,  the  aqueous  humor,  while  behin<!  it  jg 
the  main  cavity  of  the  eye,  filled  with  a  transparent, 
almost  jelly-like,  vitreous  humor.  The  lens  itself  is 
elastic.  This  circumstance  permits  of  a  change  of 
form  and,  in  consequence,  a  change  of  focus  upon 
the  retina  of  the  lens.  By  means  of  this  change  in 
form,  or  '^accommodation,''^  we  are  al^le  to  distin- 
guish between  near  and  distant  ol^jects. 

Defects  in  the  Eye.  —  In  some  eyes,  the  lens  is  in 
focus  for  near  objects, but  is  not  easily  focused  upon 
distant  objects;  such  an  eye  is  said  to  be  near- 
sighted. Other  eyes  which  do  not  focus  clearly  on 
objects  near  at  hand  are  said  to  be  far-sighted. 
Still  another  eye  defect  is  astigmatism,  which  causes 
images  of  lines  in  a  certain  direction  to  be  indistinct,  while  images 
of  lines  transverse  to  the  former  are  distinct.  Many  ner\'ous 
troubles,  especially  headaches,  may  be  due  to  eye  strain. 


Diagram  hHow- 
ing  how  the 
loiiH  chanKc^ 
its  form. 


Diagram  to  show  how  an  image  is  formed  in  the  eye ;  a,  object ;  h,  lens;  c,  image  up<.n  retina. 

How  we  See.  —  Suppose  an  object  be  held  in  front  of  the  eye; 
rays  of  light  pass  from  everj^  part  of  the  object  and  are  bnni.^lit 
to  a  focus  on  the  retina  by  means  of  the  transpaivnt  len.^.  You 
can  form  an  object  in  the  same  manner  l)y  using  a  reading  ghis.s. 
a  box  with  a  hole  in  one  end,  and  a  piece  of  white  pai>er.     Notice 


426  HUMAN   PHYSIOLOGY 

that  the  image  is  inverted.  The  same  is  true  of  the  image  on  the 
retina.  By  means  of  this  image  thrown  on  the  sensory  layer,  the 
rod  and  cone  cells  of  the  retina  are  stimulated  and  the  image  is 
transmitted  to  the  forebrain.  We  must  remember  that  the  optic 
nerve  crosses  under  the  brain  so  that  images  formed  in  the  right 
eye  are  received  by  the  left  half  of  the  forebrain,  and  vice  versa, 
'^  Effects  of  Drinks  containing  Alcohol  upon  the  Eye.  —  Through 
its  influence  upon  the  nerves  and  the  muscles,  the  continued  and 
too  free  use  of  alcohol  renders  the  eye  unsteady  and  its  adjustment 
uncertain;  the  small  blood  vessels  become  dilated,  and  the  eyes 
are  blood-shot  and  often  inflamed.  The  optic  nerve  is  frequently 
affected,  causing  dimness  of  vision,  and  specific  diseases  of  parts 
of  the  eye  may  result,  such  as  cataract  and  disorders  of  the  retina. 
The  confirmed  inebriate  is  the  victim  of  diseased  conditions  in 
which  the  sight  becomes  untrustworthy.  He  sees  horrible  visions, 
frightful,  venomous  creatures  appear  to  threaten  him,  and  he  is 
haunted  by  specters.  Under  his  imaginary  suffering  he  may  be- 
come a  raving  maniac,  and  repeated  attacks  of  the  disease  are 
likely  to  prove  fatal."  —  Macy,  Physiology. 

The  Blind  Spot.  —  Although  the  eye  is  an  accurate  organ  for  sight,  yet 
one  part  of  the  retina  is  not  provided  with  sensory  cells.  This  area,  called 
the  blind  spot,  marks  the  point  within  the  eye  where  the  optic  nerve  enters 
and  spreads  out  in  a  very  thin  layer  over  the  surface  of  the  retina. 

How  THE  Voice  is  Produced. — The  voice  box,  or  larynx,  is  well  known  to 
every  boy  as  his  "  Adam's  apple."    It  consists  of  a  box  of  movable  cartilages, 

joined  in  such  a  way  to  each  other  and  to 
muscles  so  that  by  contraction  of  certain 
muscles,  the  form  of  the  larynx  is  changed. 
Within  the  larynx  are  stretched  two  narrow 
pads  of  elastic  tissue  called  the  vocal  cords. 
It  is  by  the  vibration  of  these  cords  that  the 
sounds  of  the  voice  are  produced.  The  vocal 
cords  project  into  the  larynx  so  that  only  a 
^j     ,      J  narrow  slit  is  formed  between  the  larynx  and 

V  ocs,l  cords 

the  mouth  cavity.  This  slit  is  the  glottis. 
When  the  vocal  cords  are  drawn  into  position  for  speech,  they  vibrate,  the 
vibration  being  caused  by  a  current  of  air  driven  against  them.  This  cur- 
rent of  air  is  caused  by  movement  of  the  lips,  cheeks,  palate,  and  tongue. 
The  stronger  the  air  current,  the  louder  the  voice. 


THE  SIONSES  427 

Pitch  and  Range  of  the  Voice.  — The  pitch  of  the  voire  depends  upon 
the  length  of  the  vocal  cords  and,  hence,  on  the  size  of  tin;  larynx,  lor  this 
reason,  a  boy's  voice  changes  from  a  high  to  a  lower  pitch  during  the  period 
of  rapid  growth.  The  range  of  voice  is  about  three  octaves.  This  means  a 
difference  in  the  vibration  of  the  vocal  cords  from  eighty-eight  times  jier 
second,  in  a  low  note,  to  nearly  eight  hundred,  in  the  highest  note.  The 
range  and  actual  pitch  of  the  voice  is  controlled  by  the  muscl(?s  of  the  larynx 
attached  to  the  sides  of  the  voice  box.  When  the  tension  of  the  cords  is 
increased  by  stretching  them,  a  higher  tone  results  from  the  tighter  stretch- 
ing of  the  cord. 

Speech.  —  Articulation  or  speech  is  caused  by  the  interruption,  for  a 
very  short  period  of  time,  of  the  air  current  as  it  passes  over  the  vocal  ror<ls 
or  as  air  passes  between  the  almost  closed  lips.  Vowels  are  really  musical 
tones  produced  in  the  larynx.  Semivowels,  especially  the  n,  m,  and  ng 
sounds,  are  produced  by  a  tone  which  emanates  from  the  voice  box,  but 
with  the  soft  palate  lowered.  The  air  current  is  forced  out,  partly  through 
the  nose.  The  resonance  of  air  in  the  nose  cavity  gives  them  a  characteristic 
sound.  Consonants  are  produced  in  part  by  the  action  of  the  tongue  in 
connection  with  different  positions  of  the  lips  while  the  air  is  forced  out  of 
the  mouth.  Practice  before  a  mirror,  and  observe  the  shape  assumed  by 
the  lips  when  you  make  the  following  sounds:  p,  t,  g,  s,  j,  ch.  Record  the 
movement  in  each  case. 

''  Alcohol  and  Tobacco  as  affecting  the  Vocal  Organs.  —  As 
the  perfect  control  of  the  voice  depends  upon  the  healtliy  condi- 
tion of  all  the  muscles  connected  with  the  vocal  apparatus,  and 
upon  the  accurate  adjustment  of  nervous  force  to  their  varying 
needs,  anything  which  affects  those  muscles  or  the  nerves  affects 
also  the  voice.  Alcohol  and  tobacco  do  affect  both.  The  mucous 
membrane  of  the  larynx  is  often  much  inflamed  by  tobacco  smok- 
ing, and  especially  by  the  use  of  cigarettes.  The  inflammation 
may  extend  through  the  Eustachian  tubes,  impairing  the  hearing, 
and  into  the  bronchial  tubes,  causing  an  annoying  couixh.  A 
disease  known  as  '  smoker's  sore  throat  '  may  result.  Alcoholic 
beverages  irritate  the  throat  and  are  often  forbiilden  to  those 
cultivating  the  voice  for  singing.''  —  Macy,  Physiology. 

Reference  Books 

Some  valuable  suggestions  for  laboratory  work  in  human  physiolofO'  may  be 
obtained  from  Eddy,  Experimental  Physiology  and  Anatomy,  .Vnifrican  li<x)k  Com- 
pany, and  Peabody,  Laboratory  Exercises  in  Anatomy  and  Phyniologxj,  Honry  Holt 
and  Company.      Of  the  briefer  texts  the  best  are  Eddy,  Text-book  of  Physiology, 


428  HUMAN   PHYSIOLOGY 

American  Book  Company,  Hall,  Elementary  Physiology,  American  Book  Company, 
and  Foster  and  Shores,  Physiology  for  Beginners,  The  Maemillan  Company.  For 
the  teacher,  Foster,  A  Text-hook  of  Physiology,  The  Maemillan  Company,  is  invalu- 
able. Verworn,  General  Physiology,  The  Maemillan  Company,  gives  the  broad  basis 
to  physiology  teaching  which  is  needed  in  a  general  course  such  as  planned  in  the 
preceding  pages. 

The  numerous  Farmers'  Bulletins  oi  the  U.S.  Department  of  Agriculture  treating 
of  foods  are  readable  and  easy  of  comprehension.  Much  valuable  reference  reading 
on  foods  may  thus  be  obtained  free  of  charge.  The  following  bulletins  have  proved 
of  value  to  the  writer  for  class  work  :  Numbers  34,  74,  85,  93,  121,  and  128.  Other 
publications  of  the  Department  of  Agriculture  have  been  referred  to  in  the 
preceding  pages. 


APPENDIX 

Laboratory  Equipment 

The  following  articles  comprise  a  simple  equipment  for  a  labora- 
tory class  of  ten.  The  equipment  for  larger  classes  is  propor- 
tionately less  in  price.  The  following  articles  may  be  obtained 
from  any  reliable  dealer  in  laboratory  supplies,  such  as  the  Bausch 
and  Lomb  Optical  Company  of  Rochester,  N.Y. 

1  balance,  Harvard  trip  style,  with  weights  on  carrier. 

1  set  gram  weights,  1  mg.  to  100  g. 

1  bell  jar,  about  365  mm.  high  by  165  mm.  in  diameter. 
10  wide  mouth  (salt  mouth)  bottles,  with  corks  to  fit. 
10  25  c.c.  dropping  bottles  for  iodine,  etc. 
25  250  c.c.  glass-stoppered  bottles  for  stock  solutions. 
100  test  tubes,  assorted  sizes. 

1  test  tube  rack. 

5  test  tube  brushes. 

2  graduated  cylinders,  one  to  100  c.c,  one  to  500  c.c. 

1  package  filter  paper  300  mm.  in  diameter. 
4  flasks,  Erlenmeyer  form,  800  c.c.  capacity. 

2  glass  funnels,  one  50,  one  150  mm.  in  diameter. 

10  Petri  dishes,  100  mm.  in  diameter,  10  mm.  in  depth. 

10  stender  dishes  30  mm.  by  50  mm. 

10  pairs  scissors. 

10  pairs  forceps. 

20  needles  in  handles. 

10  scalpels. 

10  feet  glass  tubing,  soft,  sizes  2,  3,  4,  5,  6,  assorted. 

1  oblong  aquarium  jar,  10  liters  capacity. 
12  mason  jars,  pints. 
12  mason  jars,  quarts. 

420 


430 


APPENDIX 


2  specimen  jars,  glass  tops,  of  about  1  liter  capacity. 

1  alcohol  lamp. 

10  hand  magnifers,  vulcanite  or  tripod  form. 

2  compound  demonstration  microscopes  or  1  more  expensive 

compound  microscope. 
1  gross  slides. 
100  cover  slips  No  2. 

1  razor,  for  cutting  sections. 
1  mortar  and  pestle. 
300  insect  pins,  Klaeger,  3  sizes  assorted. 
10  bulb  pipettes. 

1  box  rubber  bands,  assorted  sizes. 
10  feet  rubber  tubing  to  fit  glass  tubing,  sizes  3,  5. 

1  support  stand  with  rings. 

2  books  test  paper,  red  and  blue. 

1  chemical  thermometer  graduated  to  100°  C. 
15  agate  ware  or  tin  trays  about  350  mm.  long  by  100  wiae. 
10  Syracuse  watch  glasses. 

1  spool  fine  copper  wire. 

1  gal.  95  per  cent  alcohol.     (Do  not  use  denatured  alcohol.) 

1  liter  formol. 

1  oz.  iodine  cryst. 

1  oz.  iodide  of  potassium. 

6  oz.  nitric  acid. 

6  oz.  ammonium  hydrate. 

6  oz.  benzole  or  xylol. 

6  oz.  chloroform. 

J  lb.  copper  sulphate. 

i  lb.  sodium  hydroxide. 

i  lb.  rochelle  salts. 

6  oz.  glycerine. 

The  materials  for  Pasteur's  solution  and  Sach's  nutrient  solu- 
tion can  best  be  obtained  from  a  druggist  at  the  time  needed  and 
in  very  small  and  accurately  measured  quantities. 


INDEX 

Illustrations  are  indicated  by  page  numerals  in  bold-faced  type. 


A.bsorption,  by  root  hairs,  86; 

course  of  food  after,  341; 

in  intestine,  342 ; 

in  stomach,  338; 

into  blood,  340; 

organs  of  (villi),  341. 
Accessory  fruit,  51. 
''Accommodation"    in    human    eye, 

425. 
Achene,  51,  54. 
Acid,  hydrochloric,  336; 

reaction  in  root  hairs,  93 ; 

test  for,  (note)  93. 
Acorn,  54. 

Adaptation  to   environment,    142. 
Adaptations,  for  perching,  293; 

for  seed  dispersal,  58; 

in  birds,  293,  296; 

in  moths  and  butterflies,  239; 

in  skull,  375; 

in  turtle,  286; 

in  vertebral  column,  372. 
Agassiz,  Louis,  quoted,  12, 
Aggressive  resemblance,  defined,  232 ; 

in  mantis,  232. 
Air,  in  germination,   79; 

in  starch  making,  131. 
Albumen,  test  for,  22. 
Alcohol,  a  poison,  327; 

as  a  food,  326; 

Atwater's  experiments  with,  326; 

cause  of  mental  disorders,  413; 

chemical  formula  of,  326 ; 

effect  on  bodily  heat,  398; 

effect  on  circulation,  360; 

effect  on  digestion,   343; 

effect  on  the   eye,   426; 

effect  on  the    heart,  361 ; 

effect  on  the  kidney,  393; 

effect  on  muscle,  369. 


Alcohol,  effect  on  the  nervous  sys- 
tem, 411; 

effect  on  nerve  cells,  413; 

effect  on  the  respiratory    organs, 
389; 

effect  on  the  vocal  organs,  427; 

oxidation  of,  385. 
Alcohol  poisoning,  413; 

moral  effect  of,  417. 
Algae,  blue-green,  173; 

brown,  174; 

chlorophyll  in,   173; 

economic  importance  of,    173; 

green,   174; 

red,  173. 
Alimentary  canal,  comparison  of,  in 
frog  and  man,  331; 

in  man,  330. 
Alligator,  290. 

Alligators  and  crocodiles,  290. 
Alternation  of  generations  in  ferns, 
155; 

in  mosses,  158. 
Alveoli,  function  of,  381. 
Ambulacrae,  203. 
Ambulacral  grooves,  203. 
Amoeba,  182; 

asexual  reproduction  in,  182,  183; 

changes  during  division,  182 : 

locomotion  in,   182; 

oxidation  in,   182; 

structure  of,   182. 
Amphibia,    characteristics    of,    280; 

classification  of,  285; 

examples  of,  284. 
Ampulla,  204. 
Angiosperms,  defined,  151. 
Annual  rings,  108. 
Annulus,  153. 
Anther,  31. 


431 


432 


INDEX 


Antheridium,  in  fern,  154,  155; 

in  liverworts,  159; 

in  moss,  158. 
Ants,  life  history  of,  253 ; 

talking  of,  254. 
Ants'    nest,    artificial,     252,    (note) 

253. 
Aphids,  247; 

life  history  of,  248. 
Aphids  and  ants,  249. 
Appendages,  in  crayfish,  217; 

in  frog,  371,  374; 

in  man,  372,  374. 
Apple,  study  of,  51. 
Apple  and  blossoms,  51. 
Archegonium,  in  fern,  154,  155; 

in  Liverwort,  159; 

in  moss,  158. 
Arteries,  structure  of,  353,  354. 
Arthropoda,  227. 
Ascent  of  sap,  causes  of,  113. 
Ascospores,166. 
Ascus   (plu.  asci),  166. 
Asexual  reproduction  in  coral,  201; 

in  fern,  155; 

in  hydroids,  199; 

in  mold,  160; 

in  moss,  158; 

in  paramcecium,  181. 
Astigmatism,  426. 
Asymmetry,  223,  263. 
Auricle,  352. 
Automatic  acts,  408. 

Bacteria,   diseases   caused   by,    170; 

habitat  of,  168; 

in   fermentation,  169; 

method  of  study,  169; 

relation  to  nitrogen,  94; 

size  and  form,  169. 
Bacteroids  forming  in  root  cells,  94. 
Bark,  uses  of,  109. 
Barnacles,  225,  226. 
Bast  fibers,  109. 
Bean,  study  of,  66. 
Bee,  attractions  offered  by  flower  to, 
38.    See  Bumblebee  and  Honey- 
bee. 
Beer  making,  168. 


Beetles,  economic  importance  of,  245 ; 

life  history  of,  245; 

sexual  dimorphism  in,  246; 

structure  of,  244; 

useful  to  man,  246. 
Berry,  52,  53. 
Bile,  339. 

Biology  defined,  11. 
Birds,  adaptations  in,  293,  296; 

bills  of,  295,  296 ; 

care  of  young,  298; 

classification  of,  302,  306; 

extermination  of,  300; 

feather  of,   292,  293; 

flight  of,  292; 

food  of,  299; 

harmful  to  man,  298; 

high  temperature  in,   295; 

migrations  of,   301; 

nervous  system  of,  297; 

nesting  habit  of,  297; 

nests  of,  297,  298; 

protection  of,  292; 

relationship  between  reptiles  and- 
305; 

skeleton  of,  294,  295; 

tail  of,  293. 
Birds  of  prey,  304. 
Bison,  315. 

Biuret  test,  (note)  337. 
Bladderwort,  139. 
Blade  of  leaf,  section  through,  24. 
Blastula,  formation  of,  192. 
Blood,   amount  of,   348; 

changes  of,  in  body,  357; 

clotting  of,  345; 

corpuscles  in,  344,  345,  347; 

course  of,  356,  357; 

distribution  of,  348; 

function  of,  344; 

haemoglobin  in,  346; 

Metchnikoff  on,  346; 

phagocytes  in,  347; 

plasma  in,  344 ; 

relation    of    food,   air,    and   sleep 
to,  348; 

temperature    of,   in    cold-blooded 
animals,  348; 

temperature  of,  in  man,  348. 


INDEX 


433 


Blood  cell,  189. 

Blood  serum,  345. 

Boa  constrictor,  skull  of,  289. 

Bodily  heat,  effect  of  alcohol  on,  398; 

how  produced,  348; 

regulation  of,  397 ; 

relation  to  work,  396. 
Body,  a  machine,  317. 
Bone,  structure  of,  375,  376; 

fracture  of,  379 ; 

microscopic  structure  of,  377 ; 

substances  present  in,  376. 
Bone-making  cell,  189. 
Botany  defined,  11. 
Brain,  action  of  parts  of,  407; 

effect  of  alcohol  upon,  410; 

of  frog,  402 ; 

of  man,  404,  407  ; 

necessity  of  food,  rest,  and  fresh 
air  to,  410; 

necessity  of  sleep  to,  410. 
Breathing,  hygienic  habits  of,   388; 

mechanics  of,  382 ; 

rate  of,  in  man,  383; 

relation  of  exercise  to,  389; 

relation  of  tight  clothing  to,  388. 
Bruises,  treatment  of,  360. 
Bryophytes,  151,  156. 
Buccal  cavity,  in  frog,  331; 

in  man,  332; 

openings  from,  334. 
Bud,  defined,  100; 

effect  of,  on  shape  of  tree,  102; 

lateral,  102; 

opening  of,  101,  105; 

protection  of,   105; 

structure  of,   100,  101; 

terminal,  102. 
Budding,  116; 

in  yeast,  166. 
Budding  hydra,  195. 
Bugs,  characteristics  of,  246; 

economic  importance  of,  247. 
Bulb,  119. 

Bumblebee,  37,  39,  249. 
Burns,  treatment  of,  398. 

Calorimeter,  Atwater's,  320. 
Calyptra,  157. 

hunter's  BIOL.  —  28 


Calyx,  31. 

Camlnuni,  109. 

Cap  of  mushroom,  102. 

Capillaries,  changes  in  blood  in.  356; 

passage  of  food  through  walls  of, 
355,  358; 

position  of,  355. 
Capsule,  54; 

of  moss,  157. 
Carbohydrates,  21,  318. 
Carbon,  17. 

Carbon    dioxide,    in    photo8ynthc•^i.s, 
131; 

test  for,  18. 
Carnivora,  economic  importance  of, 
314; 

examples  of,  312; 

skull  of,  313. 
Carp,  anatomy  of,  273. 
Carpel,  31. 
Cecropia  moth,  237. 
Cell,  animal,  27; 

as  a  unit,  183; 

defined,  25; 

example  of  plant  (yeast),  166; 

parts  of,  25,  26; 

sizes  and  shapes  of,  27. 
Centiped,  poisonous,  257. 
Cephalopods,  267. 
Cephalothorax,  215. 
Cercariae,  213. 
Cerebrum,  function  of,  406; 

position  of,  405. 
Chelipeds,  215,  220. 
Chemical  element,  defined,  15. 
Chemistry,  defined,  15. 
Chestnut,  55. 

Chimney  swift,  nest  of.  298. 
Chlorophyll  bodies  in  plioto>ynthesLs 

130. 
Chloropla.'^ts,  130. 
Chromo.*!omes,  25. 
Cicada,  Hfe  history  of,  247. 
Cigarettes,  j)oi.><ons  in.  .vs?. 
Cilia,  on  paranid'ciuin.  180. 
Circuhition.  effeet  of  nicoliol  on,  360; 

effect  of  exorcise  on.  360; 

in  frog,  350.  351 : 

in  frog's  foot,  353,  354. 


434 


INDEX 


Circulation  in  man,  portal,  357; 

pulmonary,  356,  357; 

systemic,  356,  357. 
Clam,  economic  importance  of,  264; 

"long,"  264; 

"round,"  264. 
Classification  of  plants,  150. 
Cleistogamous  flower,  42. 
Clitellum,  208,  211. 
Club  moss,  156. 
Cluster  cup,  165. 
Cnidoblasts,  196. 
Cocoon,  237. 

Ccelenterates,  alternation  of  genera- 
tions in,  199 ; 

classification  of,  202 ; 

di\ision  of  labor  in,  197; 

meaning  of,  195; 

organs  of  offense  in,  196. 
Coleoptera,  244. 
Colloids,  337. 
Combustion  defined,  16. 
Communal  life,  of  ants,  253; 

of  bee,  250; 

of  bumblebee,  249. 
Comparison,  between  earthworm  and 
hydra,   210; 

between  skeleton  of  child  and  of 
adult,  377; 

between  skeleton  of  man  and   of 
frog,  371; 

between  starch  making  and  mill- 
ing, 131. 
Composite  head  of  flower,  48. 
Composition  of  water,  18. 
Conjugation,  defined,  161; 

in  mold,  161; 

in  paramcEcium,  181; 

in  Spirogyra,  176. 
Connective  tissue  cells,  189. 
Coral,  asexual  reproduction  in,  201 ; 

cup,  201; 

economic  importance  of,  201 ; 

formation  of,  201 ; 

madreporic,  201. 
Coral  reefs,  202. 
Corky  layer,  use  of  (Exp.),  110. 
Corn,  production  of,  62,  63. 
CoroUa,  31. 


Corolla  in  cross-pollination,  39. 
Corpuscles,   colorless,  346,  347; 

red,  345,  346; 

tractile,  395,  419. 
Cotton,  distribution  of,  64. 
Cotton-boll  weevil,  245. 
Cotyledons,  66; 

as  foliage  leaves,  70 ; 

food  in,  67. 
Crab,  asymmetry  in  hermit,  223; 

edible  blue,  222; 

fiddler,  223; 

hermit,  223; 

metamorphosis  of,  223; 

spider,  224; 

symbiosis   between    sea    anemone 
and,  224. 
Crane,  handbill,  305. 
Crayfish,  215,  218; 

activities  of,  215; 

circulation  in,  218; 

development  of,  219; 

digestion  in,  219; 

excretion  in,  219; 

habitat  of,  215; 

mouth  parts  of,  217; 

nervous  system  of,  219; 

protective  coloration  of,  215. 
Crinoid,  207. 
Crustaceans,  classes  of,  225; 

compared  with  insects,  227; 

degenerate,  225,  226; 

habitat  of,  224; 

parasitic,  225; 

structures  common  to  all,  226. 
Cryptogams,  151. 
Crystalloid,  337. 
Cuts,  treatment  of,  360. 
Cyclops,  225. 
Cyme,  47. 
Cytoplasm,  26. 

Damsel  fly,  244. 

Deer,  Virginia,  315. 

Degenerate  crustaceans,  225,  226 

Deliquescent  trunk,  102. 

Delirium  tremens,  411. 

Dendrites,  402. 

Desert  conditions,  143,  145,  147. 


INDEX 


435 


Development,  of  earthworm,  211 ; 

of  frog,  280 ; 

of  mosquito,  242. 
Diastase,  action  on  starch  (Exp.),  73. 
Diastole,  353. 
Diatoms,  177. 
Dichogamy,  46. 
Dicotyledons,  defined,  75; 

fibro vascular  bundle  of,  109 ; 

parts  of  stem  of,  105,  108. 
Diet,  mixed  dietary  the   best,   321, 

323. 
Digestion,  defined,  330; 

in  corn  cotyledon,  75; 

in  stem,  112; 

of  starch,  334; 

organs  of,  in  man,  330; 

purpose  of,  330. 
Dimorphism  in  flowers,  46; 

sexual,  235,  236,  246. 
Dioecious  flowers,  45. 
Dipsomania,  411. 
Diptera,  240. 
Disk  flowers,  49. 
Dislocations,  379. 
Division  of  labor,  in  Pandorina,  187 ; 

in  the  hive,  250; 

in  Volvox,  187. 
Dragon  fly,  243. 
Drawing,  13. 
Drink  habit,  416. 
Drupe,  53. 

Eagle,  golden,  304. 
Ear,  care  of,  422; 

in  man,  421 ; 

inner,  421,  422; 

middle,  421 ; 

structure  of,  421. 
Earthworm,  208; 

bflateral  symmetry  in,  208; 

blood  course  of,  210; 

body  cavity,  210; 

comparison   between    hydra  and, 
210; 

Darwin  on,  210; 

development  of,  211; 

digestive  tract,  209,  210; 

feeding  habits,  209. 


Earthworm,  locomotion,  209; 

nephridia,  209,  210; 

reactions  of,  209; 

regeneration  in,  211; 

respiration  in,  211. 
Eating,  hygienic  habit.s  of,  :i42. 
Economic  iin|)ortanc(',  of  biig.s,  247; 

of  flics,  242; 

of  moUusks,  268; 

of  toads,  283. 
Economic  value  of  fruits,  62; 

of  leaves,  141 ; 

of  lobsters,  222; 

of  trees,  117. 
Ectoderm,  193. 
Ectoplasm.  182. 
Egg,  segmentation  of,  192. 
Egg  cell,  in  ferns,  154; 

in  flowers,  34 ; 

in  moss,  158. 
Elements,  chemical,  15. 
Elytra,  244. 
Embryo,  67; 

arrangement  of,  71. 
Emulsion,  eff"cct  of  pancreatic  fluid 
upon,  339; 

how  produced,  339; 

mflk  an,  339. 
Endoderm,  193. 
Endoplasm,  182. 
Energy,  sun  a  source  of,  128. 
Entomostraca,  225. 
Enzyme,  amolypsin,  339; 

diastase,  73; 

lipase,  339; 

pepsin,  336; 

ptyalin,  334; 

rennin,  337; 

trypsin,  339. 
Epidermi.s,  129.  130; 

human  skin,  'M)\.  395. 
Epithelial  cells.  189. 
Equisetuni,  156. 
Eustachian  tube,  in  frog.  279. 
Excretion,  organs  of,  391. 
Excurrent  trunk.  102. 
Experiment.  12. 
Eye,  of  insects,  230 ; 

blind  spot,  426. 


436 


INDEX 


Eye,  defects  in,  425; 
focusing,  425; 

internal  structure  of,  423,  424 ; 
longitudinal  section,  424; 
section  of  retina,  423. 

Factors,  determining  form  of  plant, 
146; 

determining  growth  of  seeds,  77. 
Fats,  in  bean,  67. 
Feather,  development  of,  293 ; 

structure  of,  293. 
Fehling's  solution,  formula  for,  21. 
Fermentation,    a    chemical    process, 
167; 

bacteria  in,  169; 

by  yeast,   166. 
Ferments,  digestive.     See  Enzyme. 
Fern,  economic  importance  of,  156; 

life  history  of,  154; 

parts  of,  152. 
Fertilization,  defined,  34; 

in  fern,  154; 

in  moss,  158; 

of  flowers,  33,  34. 
Fibrin,  345. 
Fibrinogen,  345. 
Fibro vascular  bundle,  defined,  88; 

in  dicotyledonous  stem,  109; 

in    monocotyledonous   stem,    106, 
107. 
Fiddler  crab,  223. 
Filament,  31. 
Fisheries  map,  276. 
Fishes,  appendages  of,  271 ; 

body  of,  271; 

bony,  278; 

breathing  in,  272; 

circulation  in,  274; 

classification  of,  277 ; 

digestive  system  in,  273; 

economic  value  of,  275; 

egg-laying  habits  of,  275; 

elasmo branch,  277; 

ganoid,  277; 

gills  in,  272 ; 

gill  rakers  in,  273; 

lateral  line  in,  274;     . 

lung,  278. 


Fishes,  nervous  system  of,  274; 

senses  of,  271; 

skeleton  of,  274; 

swim  bladder  in,  273 ; 

teeth  in,  272. 
Fission,  defined,  169; 

in  paramcecium,  181; 

of  a  cell,  26. 
Flagellates,  185. 
Flower,  fertilization  of,  33,  35; 

imperfect,  45; 

irregular  (sweet  pea),  36; 

parts  of,  31; 

relation  to  fruit,  66. 
Flower  envelope,  31. 
Flower  scar,  104. 
Follicle,  53. 
Food,  adulterations  in,  323; 

carbohydrates,  318; 

defined,  20; 

economy,  323; 

hydrocarbons,  318; 

inorganic,  319; 

need  of,  317; 

of  birds,  299; 

proteid,  317; 

storage  in  roots,  95; 

value  of  mushrooms,  163; 

value  of  nutritive,  322; 

waste,  325. 
Forestry,  116. 
Fowls,  303. 
Frog,  appendages  of,  279; 

development  of,  280; 

eggs  of,  281; 

eye  of,  279; 

habitat  of  green,  279; 

life  history  of,  280 ; 

protective  resemblance  in,  279; 

skin  of,  279; 

stages  of  tadpole  life,  282. 
Frond,  153. 
Fruit,  defined,  50; 

dehiscent,  53; 

distinct  from  seed,  55; 

use  of,  66. 
Fruits,  dry,  53; 

economic  value  of,  62; 

explosive,  60. 


INDEX 


437 


Fruits,  fleshy,  51 ; 

indehiscent,  54. 
Functions,   common  to  all  animals 
189; 

of  cotyledons,  69,  70; 

of  endosperm  in  corn  (Exp.),  73; 

of  parts  of  a  plant,  24. 
Fungi,  economic  importance  of,  159; 

parasitic,  164; 

poison,  163; 

sac,  166; 

shelf,  163. 
Funiculus  in  pea  pod,  50. 

Gall  bladder,  330,  339. 
Gamete,  defined,  155. 

ametophyte,  defined,  155; 

of  fern,  155; 

of  moss,  158. 
Gases  in  Uving  things,  19. 
Gastric  glands,  336. 
Gastric  juice,  acid  in,  337; 

action  of,  336,  337. 
Gastric  mill  of  crayfish,  219. 
Gastropods,  265. 
Gastrula,  formation  of,  192. 
Gemmae,  159. 
Germinating  seeds,  expansive  force 

of,  78. 
Germination,  69. 
Giant  spider  crab  of  Japan,  224. 
Girdle,   pectoral,   295,  374; 

pelvic,  295,  371,  372,  374. 
Glands,  defined,  331; 

digestive,  334,  336,  338,  339,  341 ; 

gastric,  336 ; 

intestinal,  341; 

mesenteric,  342; 

nectar,  38; 

peptic,  336; 

salivary,  334; 

sebaceous,  396; 

structure  of,  331; 

sweat,  395,  396. 
Glucose.     See  Grape  sugar. 
Glycogen,  use  of,  340; 

where  formed,  340. 
Grafting,  116. 
Grain,  56- 


Grape  .sugar,  test  ff)r,  21. 
Grasshopper,  lilood  making  in,  229, 

economic  importance  of,  230; 

eyes  (if,  230; 

food  taking  in,  220; 

life  history  of,  230; 

mouth  parts  of,  229 ; 

muscular  activity  of.  229; 

nervous  .system  of,  230; 

relatives  of,  2.30 
Guard  cells,  129,  130,  136. 
Gymnosperms,  151. 

Habit,  drink,  416; 

formation  of,  408; 

importance  of  forming  good,  400 
Hair,  follicle,  395; 

growth  of,  395. 
Hairs,  as  protection  for  leaves,  138. 
Halophytes,  145. 
Hare,  wood,  308. 
Hay  infusion,  animals  in,  179; 

plants  in,  179; 

preparation  of,  179. 
Head,  regions  of,  407. 
Heart,  in  action,  353; 

internal  structure  of,  362; 

nervous  control  of,  359; 

position  of,  351 ; 

protection  of,  351; 

size  of,  351 ; 

work  of,  353,  365. 
Heart  muscle,  364. 
Heart  wood,  114. 
Hcmiptera,  2  }(>. 
Hermit  crab,  223. 
Hibernation,  of  animals,  (note)  397; 

of  butterflies,  235. 
Hilum,  66. 

Homology,  of  part.*!  of  flower,  56. 
Honeybee,  250,  251 ; 

food  of,  252. 
Hooks,  in  seed  dispersal,  69. 
Horse,  geologic  history  of,  315; 

Osborn  on,  316. 
Horsetail  fern,  166 
House  fly,  a  pest,  241 ; 

economic  inij)ortance  of,  212; 

home  experimentvS  with,  241. 


438 


INDEX 


House  fly,  life  history  of,  24i. 

Humus,  92. 

Hydra,  development  of,  198; 

food  taking  in,  197; 

reproduction  in,  195,  197; 

structure  of,  196,  197. 
Hydrocarbons,  318; 

tests  for,  21. 
Hydroid  colony,  199. 
Hydrophytes,  144. 
Hymenoptera,  248. 
Hypha,  160,  162. 
Hypocotyl,  arched,  68. 

Ichneumons,  254. 
Indian  corn,  62. 
Inflorescence,  47, 

Inorganic  matter,  action  of  root  hairs 
on,  93; 

in  living  things,  19; 

needed  for  plant  growth,  94; 

relation  to  organic,  28. 
Insectivorous  plants,  139,  140. 
Instruments,  14,  429. 
Intestine,  absorption  in,  341,  342; 

structure  of,  340^  342; 

glands  of,  341. 
Involucre,  48. 

Joints,  as  levers,  378  ; 
ball  and  socket,  378; 
dislocation  of,  379; 
gliding,  378; 
hinge,  378; 

movement  by  means  of,  378; 
pivot,  378. 

Keel,  36. 

Key  fruit,  55. 

Kidney,  circulation  in,  392; 

effect  of  alcohol  on,  393; 

section  of,  392; 

sheep's,  391; 

wastes  given  off  in,  393. 
Knots,  104,  115. 

Laboratory  essentials,  13,  429. 
Lacteal  system,  359. 
Lacteals,  342,  359. 


Laminated  layer  of  shell,  260. 
Leaf,  compound,  124; 

cross  section  of,  130; 

dicotyledonous,  124; 

functions  of,  132; 

monocotyledonous,  124; 

heliotropism  in,  125; 

modifications  of,  124,  137,  138; 

photosynthesis  in,  133; 

respiration  in,  137; 

structure  of,  132 ; 

transpiration  in,  134; 

venation  of,  125. 
Leaf  scar  or  trace,  103. 
Leaflike  stems,  121. 
Leaves,  arrangement  of,  126; 

as  food,  141 ; 

effect  of  light  on,  125. 
Leech,  212. 
Legume,  50,  53. 
Lenticels,  104. 
Lepidoptera,  232. 
Lichens,  172; 

symbiosis  in,  173. 
Lingual  ribbon,  266. 
Liver,  330,  339. 
Liver  fluke,  213. 
Liverworts,  159. 
Lizards,  examples  of,  287,  288. 
Lobster,  development  of,  220; 

economic  importance  of,  222; 

molting  of,  221; 

North  American,  216,  220. 
Locules,  33. 
Lungs,  changes  in  air  in,  384; 

changes  of  blood  in,  385; 

human,  381 ; 

loss  from,  384; 

of  frog,  380. 
Lymph,  composition  of,  358; 

function  of,  358; 

glands  of,  359. 
Lymph  vessels,  358. 

Macronucleus,  181. 
Madreporic  plate,  204. 
Malaria,  cause  of,  185. 
Malacostraca,  225. 
Mammals,  adaptations  in,  312. 


INDEX 


439 


Mammals,  carnivorous,  312; 

characteristics  of,  310; 

examples  of,  311; 

hoofed,  314; 

orders  of,  311. 
Man,  a  mammal,  316. 
Man's  place  in  nature,  316. 
Mantle,  section  of,  260. 
Manubrium,  198. 
Marsupials,  311. 
Matter,  defined,  11; 

forms  of,  15.     See  Inorganic  and 
Organic. 
May  fly,  244. 
Medullary  rays,  108,  114. 
Medusa,  development  of,  199; 

structure  of,  198. 
Mesenteries,  201. 
Mesoderm,  193. 
Mesoglea,  193. 
Mesophytes,  145,  146. 
Metamorphosis,  defined,  227; 

in  butterfly,  233; 

in  crab,  223; 

in  frog,  280; 

in  moth,  236,  237; 

in  toad,  283. 
Micronucleus,  181. 
Micropyle,  66; 

in  ovule,  34. 
Mildews,  166. 

Milk  teeth,  dental  formula,  333. 
Milkweed  fruit,  77. 
Mimicry,  235. 
Mold,  growth  of,  160. 
Mollusca,  characteristics  of,  259. 
Mollusks,  259; 

boring  and  harmful,  266,  269; 

classification  of,  26: 

cross  section  of,  260; 

economic  importance  of,  268; 

habitat  of,  268. 
Monarch   butterfly,   Hfe   history   of, 
233; 

senses  of,  233. 
Monocotyledons,  75,  107. 
Morphology,  defined,  12. 
Mosquito,  development  of,  242;        , 

relation  of,  to  disease,  243. 


Moss,  economic  value  of,  159; 

life  history  of,  157; 

parts  of,  157. 
Moth,  adaptations  in,  239; 

cetTopia,  237; 

life  history  of,  236,  237; 

harmful  larvae  of,  238. 
Moths  and  butterflies,  comparod,  230. 
Motor    nerves,    in    striated    niu.scle 

fiber,  363. 
Muscle  cell.s,  189. 
Muscles,  and  movement,  362; 

blood  supply  to,  364; 

contraction  rate  of,  .364; 

effect  of  tobacco  on,  370; 

extensor,  362; 

flexor,  .362; 

in  leg  of  frog,  362; 

necessity  of  food  and  fre.<;h  air  for, 
366; 

relation  of  alcohol  to,  367; 

rest  and  exercise  of,  367 ; 

structure  of  involuntary,  364; 

structure  of  voluntary,  363; 

uses  of,  in  standing,  365; 

uses  of,  in  walkiiifj:,  365; 

work  done  by,  365. 
Mu.shroom,  parts  of,  162. 
Mushrooms,  food  value  of,  163; 

poisonous,  163. 
Mussel,  261; 

circulation  of  blood  in,  262; 

circulation  of  water  over  gills  of, 
261; 

early  development  of,  263; 

food  getting  in,  262; 

locomotion    in,   2()2; 

nervou.s   .■^v.^toin  of,  263; 

shell  of,  259.  260; 

structure  of,  261. 
Mycelium,  162. 
Myriapods,  258. 

Narcotics,  329,  417.     See  .\lcohol  and 

Tobacco. 
Nectar,  defined.  38. 
Nectar  jz;lan(ls.  39. 
Nectar  guidc."^,  39. 
Nectaries,  39. 


440 


INDEX 


Nephridia,  209,  210. 
Nerve  cell,  189. 
Nerve  fiber,  402. 
Nerve  unit,  403. 
Nerves,  cranial,  405; 

motor,  402,  405; 

sensory,  402,  406; 

vasomotor,  359. 
Nervous  system,  central  functions  of, 
in  frog,  403 ; 

cerebro-spinal  in  frog,  402 ; 

cerebro-spinal  in  man,  401; 

divisions  of,  400; 

general  functions  of,  400; 

sympathetic,  406. 
Neuroptera,  243. 
Nicotine,  a  deadly  poison,  329. 
Nictitating  membrane,  279. 
Nitrogen,  18; 

amount  of,  in  air  (Exp.),  19; 

needed  for  plant  growth,  94. 
Nitrogen-fixing  bacteria,  94. 
Nomenclature,  botanical,  150. 
Notebook,  use  of,  13. 
Nucleolus,  26. 
Nucleus,  25; 

in  ovule,  33,  34; 

in  Spirogyra,  175; 

in  yeast,  166. 
Nut,  54. 
Nutrients,  cost  of,  324; 

defined,  20; 

fuel  value  of,  320; 

uses  of,  319. 

Octopus,  268. 

One-celled  plants  and  animals,  183. 

Opossum,  Virginia,  311. 

Organ,  defined,  24. 

Organic  matter,  classified,  19; 

relation  to  inorganic,  28. 
Organism,  defined,  24. 
Osmometer,  potato,  90. 
Osmosis,  defined,  89; 

importance  of,  90; 

in  root  hair,  89. 
Osmotic  pressure,  90. 
Ostrich,  African,  302. 
Ovary,  31,  33;   parts  of,  32. 


Ovule,  development  of,  34; 

fertilization  of,  33. 
Oxidation,  defined,  16; 

heat  the  result  of,  17; 

in  a  match,  16; 

in  amoeba,  182; 

in  human  body,  80; 

slow  (Exp.),  17. 
Oxygen,  given  off  by  green  leaves, 
132; 

preparation  of,  16; 

properties  of,  16. 
Oyster  drill,  shell  bored  by,  266. 
Oysters,  artificial  breeding  of,  263; 

asymmetry  in  shell  of,  263 ; 

economic  importance  of,  264; 

typhoid  bacillus  in  raw,  264. 

Palisade  layer,  130. 

Palmate  venation,  123. 

Pancreas,  330,  339. 

Papilionaceous  corolla,  36. 

Pappus,  59. 

Paramcecium,  locomotion  in,  180; 

reproduction  in,  181; 

response  to  stimuli,  180; 

study  of,  179. 
Parapodia,  211. 

Pasteur's  solution,  formula  for,  167. 
Pearls  and  pearl  formation,  269. 
Pectoral  girdle,  in  birds,  295; 

in  frogs,  374; 

in  man,  374. 
Pelvic  girdle,  in  birds,  295; 

in  frogs,  371,  374; 

in  man,  372,  374. 
Perching,  adaptations  for,  293. 
Pericardium,  use  of,  352. 
Pericarp,  defined,  50. 
Perithecium,  166. 
Pepo,  52. 

Peptone,  defined,  337. 
Petiole,  126. 
Petal,  31,  38. 
Phanerogams,  151. 
Phoebe,  nest  of,  297. 
Photosynthesis,  chemical  action  in, 
133; 

compared  with  milling,  131. 


INDEX 


441 


Photosynthesis,  illustrated,  131  ; 
oxygen  and  water  the  waste  prod 

ucts  of,  132,  134; 
rapidity  of,  134. 
Physics,  defined,  15. 
Physiology,  defined,  12; 

importance  of  osmosis  in,  90. 
Pine  seedlings,  76. 
Pinna,  153. 
Pistil,  31. 

Pistillate  flower  of  com,  71. 
Pitcher  plant,  140. 
Placenta,  in  ovary,  33; 

in  pea  pod,  50. 
Plant,  a  hving,  23. 
Plant  societies,  146. 
Plasma,  composition  of,  344; 

function  of,  344. 
Pleura,  382. 
Pleurococcus,  177; 

formation  of  zoospores,  177. 
Plumule,  67. 
Pocket  garden,  82. 
Pod,  study  of,  50. 
Polar  limit  of  trees,  147. 
PoUen,  31,  32; 
amount  of,  43; 
protection  of,  46. 
Pollen  grain,  32 ; 

germination  of,  32. 
Pollen  tube,  32. 
Pollination  by  bird,  40; 
by  insect,  36,  39,  42,  43; 
by  water,  45; 
by  wind,  43; 
Darwin  on,  35; 
defined,  35; 
self,  42. 
Poly  cotyledons,  defined,  75; 

embryo  of,  75. 
Polymorphism,  235. 
Pome,  52. 
Pork  worm,  214. 
Primates,  316. 

Prismatic  layer  of  shell,  259,  260. 
Proboscis,  232. 
Proglottids,  213. 

Protective  resemblance,  in  dead-leaf 
butterfly,  239. 


Protective  rosomblanrr',  defined,  231 ; 
in  katydid,  2:U; 

in  luna  moth,  240; 

in  underwing  moth,  240; 

in  walking  stick,  231 
Proteid  formation  in  plant,  1.33. 
Proteid.s,  in  seeds,  67; 

tests  for,  22. 
Prothallus,  154; 

growth  of,  154. 
Protonema,  157. 

Protoj)lastn,  chemical  composition  <jf 
28; 

defined,  20; 

properties  of,  29; 

structure  of,  27. 
Protozoa,  and  Motazoa,  188; 

habitat  of,  184 ; 

relation  of,  to  di.sea^c,  186; 

skeleton  building  of,  184; 

use  of,  as  food,  184. 
Pulse,  cause  of,  354. 
Pupa,  formation  of,  234. 
Ptarmigan,  303,  304. 
Pteridophytes,  152. 
Pyloric  caeca,  273. 

Rabbit,  adaptations  in,  308; 

circulation  in,  310; 

nervous  system  of,  310; 

organs  of  digestion  in,  310; 

skeleton  of,  309; 

teeth  in,  308,  309. 
Raceme,  47. 
Radial  canal,  198. 
Radial  symmetry,  203. 
Radiolarian,  skeleton  of,  183. 
Rat,  310. 
Rattlesnake,  288. 
Ray  flower,  48. 
Red  Alga^,  173. 
Redia,  213. 
Reduced  leaves,  138. 
Reflex  actions,  407,  409. 
Regeneration  in  earthworm,  211. 
Reproduction,  a.^exual,  152; 

zygosporic,  101 ; 

sexual,  151. 
Reptilia,  characU-'risiicij  of,  287. 


442 


INDEX 


Reptilia,  classification  of,  291. 
Respiration,  artificial,  389; 

in  leaves,  137; 

necessity  for,  380; 

organs  of ,  in  frog,  380; 

organs  of,  in  man,  381; 

tissue,  385; 

under  nervous  control,  38 
Resurrection  fern,  148. 
Retina,  423. 
Rhizome,  153. 
Rib  and  vertebra,  373. 
Rodents,  311; 

beaver,  313; 

rabbit,  311; 

skull  of,  309. 
Root,  adventitious,  96; 

air,  97 ; 

downward  pressure  in  (Exp.),  85; 

effect  of  moisture  on  (Exp.),  83; 

fine  structure  of,  87; 

geotropism  in,  83,  85; 

growing  point  in,  85; 

osmosis  in,  89; 

parasitic,  97; 

passage  of  soil  water  within,  89 ; 

water,  96; 

cap,  86; 

pressure,  113; 

hairs,  86,  88,  93 

system,  82. 
Rootstock,  118; 

in  ferns,  153. 
Rusts,  164,  165. 

Sac,  embryo,  34. 
Salamander,  spotted,  284. 
Salt,  importance  of,  319. 
Samara,  55. 
Sand  dollar,  207. 
Sap,  ascent  of,  113. 
Saprophyte,  defined,  159. 
Saprophytic    fungi.     See    Mold    and 

Mushroom. 
Scallop,  265. 
Science  and  Matter,  11. 
Scutes,  289. 
Sea  anemone,  200. 
Sea  cucumber,  207. 


Sea  lily,  207. 

Sea  lion,  314. 

Sea  urchin,  206,  207. 

Seed  dispersal,  57. 

Seeds,  winged,  60. 

Selective  planting,  81. 

Self-control  versus  appetite,  418. 

Self-pollination,  42; 

prevention  of,  45. 
Semicircular  canals,  functions  of,  in 

birds,  293. 
Senses,  hearing,  421; 

sight,  423,  425; 

smell,  420; 

taste,  419; 

temperature,  419; 

touch,  419. 
Sensitive  leaves,  128. 
Sepal,  31. 
Seta,  209. 
Sexual  reproduction,  in  amoeba,  183; 

in  fern,  154; 

in  mold,  161; 

in  moss,  158; 

in  paramcecium,  181. 
Ship  worm,  timber  bored  by,  269. 
Shrimp,  221,  222. 
Silkworms,  American,  237. 
Silicle,  54. 
Silique,  54. 
Skeleton,  growth  of,  376; 

hygiene  of,  377 ; 

in  adult  and  child,  377; 

in  frog  and  man,  371 ; 

of  dog,  309; 

structure  of,  371; 

uses  of,  371. 
Skin,  an  organ  of  excretion,  391,  396; 

an  organ  of  sensation,  395,  419; 

glands  in,  395; 

importance  of  cleanliness,  398; 

importance  of  proper  clothing,  398 : 

layers  in,  394,  395; 

structure  of,  395. 
Skull,  bones  in  man,  375 ; 

in  man  and  frog,  374; 

of  dog,  313. 
Sleep  movements,  127. 
Snakes,  adaptation  in,  289. 


INDEX 


44:'. 


Snakes,  feeding  habits  of,  289; 

locomotion  in,  289; 

poisonous,  290. 
Snails,  activities  of,  265; 

breathing  in,  267; 

development  of,  267 ; 
.  European,  266; 

feeding  habits  of,  266; 

forest,  266; 

lingual  ribbon,  266; 

senses  of,  267 ; 

variability  in  shell  of,  265,  266. 
Soils,  composition  of,  91; 

favorable  to  evaporation,  91 ; 

organic  matter  in,  92; 

water  in  (Exp.),  91; 

weathering  of,  92. 
Sorus,  153, 

Sound,  character  of,  422. 
Sparrow,  English,  301; 

white-throated,  303. 
Speech,  formation  of  sounds,  427. 
Spermatophytes,  defined,   151. 
Sperm  cell,  in  flower,  32; 

of  fern,  155; 

of  hydra,  197; 

of  moss,  158; 

r61e  in  fertilization  of  egg,  33. 
Spider,  care  of  eggs  and  young,  258; 

structure  of,  256. 
Spider  crab,  224. 
Spider's  web,  forms  of,  256,  257 ; 

use  of,  256. 
Spike,  48. 

Spines,  in  seed  dispersal,  58. 
Spiracle,  229. 

Spirogyra,   formation   of   zygospore, 
176; 

structure  of,  175. 
Sponge,  glassy,  193 ; 

development  of ,  192; 

horny  fiber,  193; 

limy,  191; 

relation  to  environment,  193; 

simple,  191. 
Sponges,  classification  of,  193. 
Sporangium,  in  fern,  153; 

in  mold,  160; 

in  moss,  157. 


Spore,  defined,  152; 

in  fern,  \'hi; 

in  molfl,  152,  160; 

in  moss,  157. 
Spore  formation  in  yeaat,  167. 
Spore  print,  162 
Sporidia,  165. 
Sporophyte,  of  fern,  155; 

of  moss,  157. 
Sprains,  379. 
Squid,  267 
Stamen,  31,  38; 

diadeljjlKHi.-;,  36. 
Staminute  flower,  of  corn,  71; 

of  squash,  45. 
Standard,  36. 

Starch,  non-osmosis  of,  112 
Starch  grains,  67. 
Starch  test,  21. 
Starfish,  development  of,  206; 

food  of,  205 ; 

method  of  locomotion,  204; 

nervous  system,  204; 

organs  of  breatlliIlL^  205; 

regeneration  in,  206; 

skeleton  of,  203. 
Stem,  compared  with  root,  98; 

dicotyledonous,  105, 108; 

digestion  in,  112; 

efi"ect  of  gravity  on,  85; 

effect  of  light  on,  98; 

form  of  food  in,  112; 

heliotropism  of,  99; 

monocotyledonou.^^.   1()(»,  108; 

passage  of  fluid  in,  110,  111; 

position  of  buds  on,  102. 
Stigma,  31,  33,  38: 

of  wind-poUinatcd  fl<twor,  44. 
Stimulant,  defined,  325. 
Stinuili,  response  to,  in  paranurc-iuin. 

180. 
Stipe,  162. 
Stipule,  123.  124 

Stoma,  129,136;  in  transpiration.  136 
Stomach,  glands  of,  336; 

movcnient  of  walls  of.  337; 

of  frog,  3.36; 

of  man,  336. 
Storage  in  st^Mus,  118. 


444 


INDEX 


Striated  muscle,  363,  364. 

Strophiole,  66. 

Struggle  for  existence,  61. 

Style,  31,  33. 

Suffocation,  389. 

Sugar,  osmosis  of,  112. 

Sundew, 140. 

Swarming,  252, 

Sweat  glands,  structure  of,  395,  396 ; 

use  of,  396; 

under  nen^ous  control,  397. 
Sweeping  and  dusting,  387. 
Symbiosis,  in  lichens,  173; 

between   crab  and  sea  anemone, 
224. 
Symmetry,  in  flower,  41. 
Sympathetic  system,  337. 
Systematic  botany,  150. 
Systole,  353. 

Tactile  corpuscle  or  organ,  395,  419. 

Taste  buds,  420. 

Teeth,  dental  formula,  333; 

in  frog,  331; 

in  man,  332; 

internal  structure  of,  333. 
Teleutospore,  165. 
Temperature,  in  germination,  80. 
Tendrils,  120. 
Tern,  common,  306. 
Testa,  66. 
Tetanus,  171. 
Thallophytes,  151,  159. 
Thallus,  142. 
Tissue,  defined,  25; 

cells,  189. 
Tissues  and  organs,  188. 
Toad,  economic  value  of,  283; 

field  work  on,  283; 

horned,  288; 

tadpoles,  283. 
Tobacco,    effect   of,  on    circulation, 
361; 

effect  on  muscles,  370; 

relation  to  respiration,  386,  389; 

use  of,  329. 
Tortoise,  box,  287. 
Trachese,  229; 

structure  of,  381. 


Transpiration,  ettect  of,  within  stem 
(Exp.),  137; 

experiment  showing,  134; 

regulation  of,  136; 

water  lost  by  (Exp.),  135. 
Trichina,  213,  214. 
Trimorphic  flower,  46. 
Tube  feet,  203. 
Tuber,  118,  119. 
Tubercles,  in  infected  lungs,  171 ; 

on  roots  of  a  legume,  96. 
Tuberculosis,  171. 
Tumble  weed,  60. 
Turtle,  mud,  286; 

painted,  286; 

spotted,  286. 
Turtles,  adaptations  in,  286. 
Tussock  moth,  238. 
Tympanic  membrane  in  frog,  279. 
Typhoid,  160,  170. 

Ungulates,  even-toed,  315; 

hoofed,  314; 

odd-toed,  315. 
Univalve,  265. 
Umbel,  48. 
Upper  limbs,  in  frog,  371,  374; 

in  man,  372,  374. 
Urea,  393. 
Uredospore,  165. 
Urine,  393. 

Uriniferous  tubules,  392. 
Urino-genital  system  of  frog,  391. 

Vacuole,  contractile,  180,  181,  182. 

Vacuole,  food,  180. 

Valves,  in  human  heart,  352 ; 

in  human  veins,  356. 
Vegetation,  in  temperate  zones,  149; 

of  cold  regions,  147; 

of  tropics,  148. 
Veins,  valves  in,  356; 

function  of,  355; 

structure  of,  355. 
Venation,  palmate,  123; 

parallel,  124; 

pinnate,  125. 
Ventilation,  in  sleeping  rooms,  388; 

need  of,  387 ;    proper,  387. 


INDEX 


445 


Ventricle,  352. 

Venus's  flower  basket,  193. 

Venus's  flytrap,  139. 

Vermiform  appendix,  342. 

Vernation,  105. 

Vertebra,  structure  of,  in  man,  372, 

373. 
Vertebral  column,  adaptations  in,  372. 
Villus   (plu.  villi),  function  of,  341; 

structure  of,  341. 
Vocal  cords,  426. 
Voice,  how  produced,  426; 

pitch  and  range  of,  427. 
Volvox,  colony  of,  187. 

Waders,  304. 
Walking,  365. 
Walking  stick,  231. 
Warning  coloration,  234. 
Wasp,  digger,  249; 

solitary,  249,  250. 
Wasp  nest,  251. 
Wastes,  in  human  body,  393. 
Water,  amount  lost  through  kidney, 
393; 

amount  lost  through  lungs,  384 ; 

effect  on  dry  seeds,  78; 

impure,  325; 

in  germination,  78; 

in  living  thiii|;s,  19. 


Water  supply,  ofToot  of,  on  plan  Us,  11  .i. 

Wax,  in  tlio  ear,  422. 

Wheat,  production  of,  63. 

Winding  stair,  use  of,  2r)7. 

Wings,  36. 

Wood,  ccorioniic  vahic  <>(,  117; 

method  of  cutting,  115; 

structure  of,  114. 
Work,  daily,  of  heart,  3r)3; 

effect  of  alcohol  on  muscular,  307; 

muscular,  36.'). 
Worms,  cliivssi  11  cation  of,  214; 

flat,  212 ; 

sand,  211; 

round,  214; 

segmented,  211; 

tape,  213; 

unscgmented,  212. 

Xerophytes,  144. 

Yeast,  spore  formation  in,  167; 
growth  of,  166; 
economic  value  of,  166. 

Zoology,  defined,  11. 
Zoospores,  formation  of,  177. 
Zygospore,  in  Spirogyra,  176; 
in  mold,  161. 


^-  t.  State  ColUg 


CHEMISTRIES 

By  F.  W.  CLARKE,  Chief  Chemist  of  the  United  States 
Geological  Survey,  and  L.  M.  DENNIS,  Professor  of 
Inorganic  and  Analytical  Chemistry,  Cornell  University 


Elementary   Chemistry     .  ^l.io 


Laboratory  Manual     ,      .  jJ5o.5o 


THESE  two  books  are  designed  to  form  a  course  in 
chemistry  which  is  sufficient  for  the  needs  of  secondary 
schools.  The  TEXT-BOOK  is  divided  into  two  parts, 
devoted  respectively  to  inorganic  and  organic  chemistrv. 
Diagrams  and  figures  are  scattered  at  intervals  throughout  the 
text  in  illustration  and  explanation  of  some  particular  experi- 
ment or  principle.  The  appendix  contains  tables  of  metric 
measures  with  English  equivalents. 

^  Theory  and  practice,  thought  and  application,  are  logically 
kept  together,  and  each  generalization  is  made  to  follow  the 
evidence  upon  which  it  rests.  The  application  o{  the  science 
to  human  affairs,  its  utility  in  modern  life,  is  also  given  its 
proper  place.  A  reasonable  number  of  experiments  are  in- 
cluded for  the  use  of  teachers  by  w^hom  an  organized  laboratory 
is  unobtainable.  Nearly  all  of  these  experiments  are  of  the 
simplest  character,  and  can  be  performed  with  home-made 
apparatus. 

^  The  LABORATORY  MANUAL  contains  127  experi- 
ments, among  which  are  a  few  of  a  quantitative  character.  Full 
consideration  has  been  given  to  the  entrance  requirements  of 
the  various  colleges.  The  left  hand  pages  contain  the  experi- 
ments, w^hile  the  right  hand  pages  are  left  blank,  to  include 
the  notes  taken  by  the  student  in  his  work.  In  order  to  aid 
and  stimulate  the  development  of  the  pupil's  powers  of  observa- 
tion, questions  have  been  introduced  under  each  experiment. 
The  directions  for  making  and  handling  the  apparatus,  and 
for  performing  the  experiments,  are  simple  and  clear,  and  are 
illustrated  by  diagrams  accurately  drawn  to  scale. 


AMERICAN     BOOK     COMPANY 


r-^i^ 


HOADLEWS    NEW     IMHSICS 

By   GEORGE  A.    HOADLEY,  C.  K.,  Sc   I).,  I'rotessor 

ot  Physics,  Swarthmorc  College. 


Elements  of  Physics  (Text-hook) 
Laboratory  Handbook  . 


Si. 


THIS  text-book  is  straightforward  and  concise.  It  tells 
only  what  everyone  should  know,  and  it  covers  all  co! 
lege  entrance  requirements  in  physics.  The  funda- 
mental principles  are  presented  in  a  logical  order.  The 
topics  have  been  selected  with  the  greatest  care.  The  treat- 
ment is  clear  and  simple,  practical  and  interesting.  The  in- 
timate relation  between  everyday  life  and  applied  phvsics  is 
made  plainly  evident. 

^  The  problems  also  are  practical  •  they  deal  with  real 
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happened,  rather  than  upon  imaginary  cases.  Important 
physical  laws  are  verified  by  well-arranged  demonstrations. 
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of  the  book  make  it  easy  for  the  student  to  verify  the  accuracy 
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to  works  on  physics  or  are  from  the  photographs  of  real  appli- 
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^  The  book  meets  the  requirements  of  the  New  York  and 
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sociations of  Teachers  of  Physics. 

^1  The  Laboratory  Handbook  contains  sixty-two  experi- 
ments, selected  with  care,  and  eminently  practical.  The 
directions  are  simple  and  clear,  the  apparatus  required  no- 
elaborate.  Throughout,  the  student  is  trained  to  profit  from 
his  observations,  to  exercise  his  ingenuity,  and  to  depend  upon 
himself. 


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U56) 


EDDY'S     PHYSIOLOGY 

COURSE 

By   WALTER    H.    EDDY,    Chairman    of  Department  of 
Biology,  High  School  of  Commerce,  New  York  City. 


Text-Book  of  General  Physiology ^1.20 

Experimental  Physiology  and  Anatomy 60 


THIS  course,  consisting  of  text-book  and  experimental 
work,  places  the  study  of  physiology  where  it  properly 
belongs — in  the  laboratory.  It  is  therefore  suited  for 
use  in  the  most  modern  schools  and  by  the  most  progressive 
teachers.  Although  intended  especially  to  supply  all  the 
material  required  by  the  New  York  State  syllabus,  its  topical 
arrangement  and  division  of  subject  matter  adapt  it  equally  to 
schools  in  other  localities. 

^  The  laboratory  manual  contains  simple  practical  exercises 
which  afford  information  of  much  value  supplementing  the 
pupil's  daily  experience.  The  directions  for  performing  the 
work  are  ample  and  easily  grasped. 

^  The  text  supplements  the  laboratory  exercises,  and  enables 
the  pupil  to  complete  and  round  out  the  information  he  has 
gained  by  experiment.  At  the  same  time  it  aids  the  teacher 
in  directing  the  experimental  inductions  and  gives  unity  to 
the  work. 

•jl  Both  text  and  manual  treat  physiology  as  a  study  of 
function  in  Hving  forms  and  as  a  part  of  the  training  in 
biologic  science  and  not  as  an  isolated  subject.  The  physi- 
ological processes  are  presented  as  activities  common  to  all 
living  matter,  and  much  space  is  given  to  the  comparative 
study  of  function  in  the  animal  forms  other  than  man.  The 
teaching  of  recent  biological  progress  is  recognized  in  the 
prominence  given  to  the  cell  and  protoplasm  as  the  structural 
and  physiological  units. 


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